The Queensland Court of Appeal considered the point recently in Cook v Commissioner of Police  QCA 118, and is helpful because it's one of the few Court of Appeal decisions on the defence applying to driver's licences.
Mr Cook's driver licence was suspended due to an accrual of demerit points, similar to the Victorian scheme under s 25 of the Road Safety Act. He claimed at court (first at the Magistrates' Court, and then on an application to appeal, at the District Court) he didn't realise his licence suspension would occur automatically after incurring a further infringement.
He relied, in part, on s 24 of the Criminal Code, which provides:
24 Mistake of fact
(1) A person who does or omits to do an act under an honest and reasonable, but mistaken, belief in the existence of any state of things is not criminally responsible for the act or omission to any greater extent than if the real state of things had been such as the person believed to exist.
(2) The operation of this rule may be excluded by the express or implied provisions of the law relating to the subject.
The Court of Appeal rejected his contention he had made a mistake of fact, deciding that his mistake was one of law. And without explicitly saying so, the Court also seemed to suggest the mistake wasn't reasonably held in any event.
 The applicant is correct, in my view, in saying that even in an automatic cancellation case, there may be scope for mistake of fact about whether the underlying events which will give rise to cancellation have occurred. Such a mistake might arise in relation to whether conduct attracting demerit points had in fact occurred; or how the Chief Executive had actually exercised what appears to be a discretion in relation to the recording of points against a traffic history; or whether a choice to be of good behaviour rather than have the licence suspended had successfully been notified to the Chief Executive. The allocation of demerit points, however, is automatic, being legislatively deemed to occur on the day of the offence.
 The only mistakes adverted to by the applicant at first instance were a general belief that his licence was not suspended, because he did not appreciate that he had accrued sufficient demerit points for that to occur, and a more specific notion that renewal of his licence meant that his demerit points would be expunged. He did not ascribe any particular belief concerning any element of the offence to his receipt of the SPER letter. The passage on which he relied, set out at  above, shows, at the highest, that he had attributed the police officer’s actions to that letter, rather than to the prospect that his accrued demerit points had caused suspension of his licence. The notion that renewal of a licence meant the removal of accrued demerit points was, on any view, a mistake of law. The applicant’s failure to appreciate that his demerit points had reached a point at which his licence could be suspended falls short of a positive mistake. In any event, it turns on a lack of understanding of the legal consequences of the successive offences, of which he was aware, in resulting in an accumulation of points beyond the permitted limit.
Curiously, the decision did suggest that the defence can occur in some circumstances, but I must confess I struggle to see how they might occur, and why they would be mistakes of fact rather than law in any event. There is no 'discretion' for VicRoads to record demerit points, but it could perhaps be argued that it is unfair to the extent of being an abuse of process for it to not record points in a timely manner, relying on National Car Parks Ltd v Baird (Valuation Officer)  1 All ER 53;  EWCA Civ 967 at  –  per Dyson LJ. But even that seems limited, given there's now a 12-month window of opportunity for VicRoads to act on points under reg 73(3) of the Road Safety (Drivers) Regulation 2009.