I had the opposite experience in the thread headed St Michaels Court. The first PCN specifically referred to POFA. I challenged on the basis of imprecise location and then got a second PCN that failed to address the matter of location at all but specifically said it was not being issued under POFA. At this point I said "well, if you are not making the claim against me - the RK - under POFA then address it to the driver, but I am under no obligation to name him/her".
When it went to POPLA the adjudicator dismissed the second PCN and the reference to it not being under POFA as a "typo" despite this being effectively repeated in two other places and relied entirely on the first one. The adjudicator did not, it seems, go back to the PPC to ask if the second letter did indeed contain a "typo".
So it seems as though both PPCs and POPLA can decide at will whether a non-POFA compliant PCN succeeding a POFA compliant one - or vice versa - prevails. Hence my original enquiry in the Purley Way case as to whether the first PCN or communication had to mention POFA in order for it to be invoked. As a read of St Michael's Court will show I was pretty familiar with POFA but did not know the answer to this last point. It seems from the correspondence between Nosy Parker and b789 that it is not entirely clear. However I got off Purley Way because the original PCN did not mention POFA, the PPC accepted that I could not be liable in the absence of a POFA compliant PCN, and they did not send a second one.