Patent applications can claim priority to an earlier filed domestic or foreign patent application, assuming certain requirements are met. The priority claim enables the application to have an earlier effective filing date for prior art and other purposes. Maintaining proper priority can be critical to a patent's validity. Yet, a proper priority claim has certain formalist requirements that can be easily overlooked.

A recent case involving Apple at the PTAB illustrates the potential pitfalls with complex priority claims.  The patent, US 7,643,168, relates to image capturing and was challenged by Apple.  The Federal Circuit affirmed the PTAB's conclusion that the application improperly identified the type of continuing application that was filed and thus priority was lost. Part of the problem was a failure to include the full chain of priority on the Application Data Sheet (ADS).  Below is an except of the form. The applicant did not use the "Add" button to include the second link in the priority chain, but merely included the last step in the chain.  Namely,  the ’470 application was a divisional of a prior application, and the applicant needed that earlier date to save the patent. But because it was not listed, no such priority was available. The Applicant attempted to save the priority by relying on the specification.  But, not only was the ADS defective (as it only had the first link in the chain), but the priority claim in specification was also unclear.  In the end, the patent was lost.

While it looks like the form can only include one priority claim, it expands each time you use the "Add" button.  The full chain of priority can therefore always be included in the ADS.