A very useful discussion of the case can be found in R v Dent  QCA 247 between 14 and 20 (with further comments about sentencing at 25).
The Facts in Giretti
Mr and Mrs Giretti owned a massage parlour in Geelong and over the course of a year sold heroin to their employees, occasionally giving them payment for their services in heroin.
The Girettis appealed after being convicted of trafficking by a jury. One ground advanced on the appeal was that the charge was duplicitous as it clearly revealed more discrete offences than charged.
On first blush it would seem obvious that the charges would be considered invalid, at least in need of particularisation. The evidence at trial disclosed (as the Crown intended it to) numerous instances where transactions of heroin took place. The appellants relied on the case of R v Trotter (1982) 7 A Crim R 8, which discussed the principle of charges which were void for uncertainty.
The Court (Crockett, Gray and Ormiston JJ) determined that trafficking drugs can be alleged as either a single event, or can be a continuing offence. Where alleged as a continuing offence there may be a number of discrete offences which go towards establishing the course of conduct. Crockett and Gray JJ formed the majority, dismissing the Girettis' appeal. Ormiston J dissented, opining that the conviction ought to have been quashed based on inadequate jury directions.
Crockett J first discussed the single transaction analysis, a way of bundling together criminal acts closely related in time and geography [at 22]:
The cases show that in certain fact situations drafting a presentment so as to accommodate to these requirements can prove difficult. In Ballysingh the indictment charged the appellant in one count with theft of four items which had each been stolen from a different section of a large department store. But for counsel's consents having been given to the charges being so pleaded, the Court of Criminal Appeal considered it to be a case for individual counts for each of the four articles stolen. This conclusion would, however, appear not to be correct in the light of later authority. Otherwise where would the analysis end? Is a person who picks up and takes away half a dozen tomatoes from a shop display case to be charged with six counts of theft? The Divisional Court in Jemmison v Priddle  1 QB 489 held that it was permissible to allege in an information one "activity" even though that activity involved more than one act each of which could be labelled illegal. In that case it was said that, as the matters complained of occurred within a few seconds and in the same geographical location, they were components of a single activity. In DPP v Merriman  AC 584 Lord Morris at p.593 approved of the course adopted in Jemmison's Case. He thought that the difficult questions that might arise "are best answered by applying common sense and by deciding what is fair in the circumstances". In the same case Lord Diplock said (at p.607) that where -"a number of acts of a similar nature committed by one or more defendants were connected with one another, in the time and place of their commission or by their common purpose, in such a way that they could fairly be regarded as forming part of the same transaction or criminal enterprise, it was the practice, as early as the eighteenth century, to charge them in a single count of an indictment."
In Giretti, it was clear that this test was not satisfied. The acts comprising the trafficking occurred on different days in different places, involving different participants.
His Honour continued,
But an offence may be "continuous" in a quite different and less "constructive" way. It is a submission by the respondent that counts 2, 3 and 5 deal with such offences that brings me to the second matter to which consideration of ground 3 requires attention to be given. That question is whether the offence of trafficking (other than as it is statutorily defined) is by its very nature a continuing offence. The definition of the expression in the current Act certainly refers only to single acts. It is, however, an inclusive definition. There is nothing in its terms to preclude the adoption of the construction for which the respondent contends.
In my opinion the term "traffick" does connote a continuing activity. The Shorter Oxford Dictionary includes among the meanings of the verb - "To carry on or trade in, to bring and sell; to deal in; often with sinister implication." Such a construction is consistent with such observations as there are in the reported cases. The tenor of the judgment of Anderson, J in Falconer v Pedersen  VR 185 (a decision often referred to with approval by appellate courts) is that it is immaterial for the purpose of proof of the offence whether the defendant's conduct was or was not an isolated act. His Honour pointed out that the expression "traffic" was not to be given a limited meaning. See, too, R v Holman  VR 471.
Gray J reached the same conclusion by taking a plain, literal interpretation to the wording of the legislation. After first describing the meaning of traffick at some length, he queried [at 25],
Are there any practical objections to such a broad definition? No doubt as a matter of form counts relating to isolated or finite events are easier to draft, and certainly they describe easier concepts for a jury to grasp. "Continuous" offences are, however, well known to the law, although such learning as exists relates more to summary offences and the problems of continuing penalties: cf. R v Industrial Appeals Court ex parte Barelli's Bakeries Pty Ltd (1965) VR 615 and R v Industrial Appeals Court ex parte Circle Realty Pty Ltd (1980) VR 459. Nevertheless, they are by no means unknown as indictable offences, especially in cases of conspiracy, public nuisance and certain statutory offences; cf DPP v Doot  AC 807 and R v G, F, S & W  1 NSWLR 31 at pp. 43-44. Nor is it of consequence that the continuing offence may in fact consist of a series of activities or transactions which can each be described in themselves as acts of trafficking, so long as the jury is properly directed as to the significance of the individual transactions alleged to evidence the continuing offence.
Crockett, J has referred to a number of the cases where a series of acts have been held to be a single activity, transaction or enterprise, whether carried out over a period of a few minutes or many days: see, e.g., Jemmison v Priddle (1972) 1 QB 489, DPP v Merriman (1973) AC 584 at pp. 593, 597 and R v Wilson (1979) 69 Crim App R 86. These cases, which involved claims of what has been called "hidden" duplicity, are examined in detail at paragraphs 1-57 to 1-62 of Archbold, Criminal Pleading and Practice (43rd ed.).
Without wishing to deny the possibility of a single count covering a series of sales or deliveries of drugs at the same place within the course of, say, an hour, it is clear that in the present case the activities alleged against the applicants over the period stated in count 2 were many and varied and could not be said to form part of a single activity or transaction or, possibly, enterprise within the meaning of those cases. It is argued on behalf of the respondent that there was indeed a continuous enterprise in the present case, but that was clearly an enterprise in the sense of a continuing trade of dealing or trafficking in drugs, "continuing" not in the sense that the activities took place at all times throughout the period, but in the sense that they took place with the necessary degree of regularity and system to amount to a business or trade in heroin.
That argument was accepted by the majority and the appeal was dismissed.
The Court in Giretti found that trafficking could be made out based on a single transaction (or even no transaction, such as preparation for sale) but could equally belong to the class of continuous offences. Common examples include consorting, stalking or persistent sexual abuse of a child.
(The late David Ross QC's 2005 article in the Deakin Law Review, from which these examples are drawn, is an authoritative discussion of continuing offences.)
The Court of Appeal in Meng Kok Te v R (1997) 97 A Crim R 386 rejected an appeal ground claiming that the High Court had disapproved of Giretti in Walsh v Tattersall (1996) 188 CLR 77. (Giretti was referred to in Walsh v Tattersall, but not disapproved, and the nature of the charges alleged in each case was distinguished). Giretti-style presentments have been tacitly approved by the Court of Appeal since. In Djukic v The Queen  VSCA 65 the Court strongly advised that plea agreements on Giretti-trafficking should be put in writing to avoid later disputes about the scale of the offending.
Later cases have expanded the principle to hand the prosecution further forensic advantages. It's permissible for the prosecution to charge a so-called Giretti count and also lay individual counts of trafficking which comprise the alleged course of trafficking. (Section 51 of the Interpretation of Legislation Act prevents both the individual and the 'umbrella count' being found proven.) The Giretti count may still succeed even if some of the individual acts are not proved.
Trafficking in other kinds of drugs is admissible toward the inference that trafficking in a particular kind of drug took place: R v Komljenovic  VSCA 136. A disparity between dates alleged and evidence given will not necessarily lead to injustice: R v Lee  VSC 121.