I'm not sure which film this is, but from the history of Jess Franco I would conjecture that this is some kind of re-release or revised print.  It wasn't until Video Watchdog really made Franco a well known cult figure in its early issues in the 1980s that most people had the faintest sense of who Jess Franco was any more than J.P. Johnson.  So there'd be no particular attraction to adding his name to an older film until after that point. Furthermore, due to snootiness about local filmmakers, Spanish and Italian directors frequently worked under English pseudonyms so they looked like higher-quality imports rather than the usual cheapie shot in 3 days sleaze (a hallmark of Franco's films).

Anyway, my reading of this credit is that originally the credit onscreen read "J. P. Johnson" and that it was revised (possibly in the transfer to the DVD) to add the quotation marks and the Jess Franco reference.  The "J.P. Franco" on the back cover is probably a typo that combines the two.

Again, this is all conjecture, but I can't see any way to make "J. P. Johnson" a nickname.  So I don't think the middle-name rule applies at all.

The Lina Romay thing is weird and probably impossible to figure out for certain.  She was credited with directing a lot of films, both under her own name and her porn pseudonym, Candy Coster, but many Franco authorities seem convinced that they're actually Jess's work.  Whether Romay ever sat in the director's chair at all is to my mind open to question.  Given that Candy Coster is well-established as her nom de porn, I guess we have to give her the benefit of the doubt that it is her directing unless we find some irrefutable evidence to the contrary (say, interviews with Romay and Franco, commentaries, etc.).

Quoting Corne:

Quote:
Actually, that rule is talking about actors. The director is part of the crew.

AAAAhhhhhhh!!!!!!