When a complete patent application is filed, it typically claims priority to one (or more) earlier applications (a priority application) filed up to 12 months earlier. Each claim is entitled to a priority date, which could be the date of filing of the priority application or the date the complete patent application was filed. This priority date is important, as it sets the date for consideration of novelty and inventive step. Any publication after the priority date cannot affect the novelty or inventive step of a patent claim. The priority date of a claim could therefore be of vital importance if there is a relevant publication between the date of filing the priority application and the complete patent application. Depending on the subject matter recited in the claim, a claim could potentially be entitled to more than one priority date. How is the priority date of a claim determined?
Under both the Patents Act 1953 and the Patents Act 2013, the priority date of a claim is determined by assessing which priority application provides fair basis for the claimed subject matter (1953 Act) or discloses the subject matter that supports the claim (2013 Act). If there is more than one such priority application, the claim takes the date from the earliest disclosure that meets these criteria. For example, if there are two priority applications and both support the subject matter of the claim then the claim would be entitled to the earliest date. If only the later priority application supports all of the claimed subject matter, then the later date would apply. In any event, in New Zealand a claim can have only one priority date.
The situation is different in Australia – a claim may have multiple priority dates if it defines separate forms of the invention (Patents Act 1990). How the priority date(s) of a claim is determined was considered recently in Nichia Corporation v Arrow Electronics Australia Pty Ltd  FCA 699.
Nichia Corporation (Nichia) sued Arrow Electronics Australia Pty Ltd (Arrow) alleging infringement of a claim of its Australian patent (claim 3, which was dependent on claim 1). Arrow countered that claims 1 and 3 were invalid. The patent was filed in July 1997 and claimed priority to two earlier applications, filed in July and September 1996, respectively.
The applicable law (section 43(3) of the Patents Act 1990) states “where a claim defines more than one form of an invention, then, for the purposes of priority date determination, the claim must be treated as if there were a separate claim for each form of the invention that is defined”.
The Court therefore had to determine whether claims 1 and 3 defined more than one form of the invention. According to Australian case law, to have multiple priority dates a claim must allow for alternatives – i.e. the claim could be regarded as two (or more) notional claims. Nichia submitted that claim 1 provided distinct selection steps that resulted in more than one form of the invention being defined. In essence, Nichia contended that the selection steps in the claims “are a convenient summation of what is, in effect, a number of separate claims to different combinations”. Nichia said that some forms of the invention defined in claim 1 were entitled to a priority date of July 1997 (i.e. the filing date of the complete patent application), some were entitled to a September 1996 priority date (based on one of the priority applications) and some to a July 1996 priority date (the other priority application). Nichia also contended that claim 3 defined more than one form of the invention and that each form of the invention in claim 3 was entitled to a July 1996 priority date.
On the other hand, Arrow submitted that claim 1 did not provide alternatives; it only provided variants which were all within the scope of one form of the invention. Arrow asserted that claim 1 did not define separate forms of the invention and so could not be regarded as more than one notional claim. It argued that the subject matter of claim 1 was only entitled to the July 1997 patent filing date, because the full invention of claim 1 was not disclosed in any of the priority documents. Arrow also said that because claim 3 depends from claim 1 it is only entitled to the same priority date as claim 1.
The Court agreed with Nichia and considered that claim 1 and claim 3 both contained “discrete and express selection steps” and therefore “envisage and provide for different forms of the invention”. Claim 1 was therefore entitled to multiple priority dates as set out by Nichia. Claim 3 was found by the Court to be fairly based on matter disclosed in the July 1996 priority application and therefore was entitled to a July 1996 priority date.
The finding by the Court that claim 3 has a July 1996 priority date is significant because it knocks out any potentially relevant art published after July 1996 and therefore may influence the outcome of Arrow’s invalidity counterclaim.
If a similar situation arose in New Zealand, it is likely that claim 1 would only be entitled to the latest priority date available, July 1997 (i.e. the filing date of the complete patent application). This is because in New Zealand a claim can only have one priority date, and the complete patent application filed in July 1997 was the only document to disclose all the alternatives falling within claim 1.