I have seen WP NP and VP blocks as well as VP chassis numbers as well, where new subframes were fitted to cars after accident damage.
That was definitely the case. I was reading up on another club's newsletter (can't remember which club) about a year ago where a member's 1959 FC had been re-registered as a 1961 car. Turns out the FC had to be rebodied after a bad accident in 1961 so the FC was rebodied and the Police stamped 'P' to the chassis after Police inspection. It seems that if Police at the time had to inspect and certify a rebodied car, they would also re-register it.
Cheers ...... Pete