Both Mark McGee and I separately saw clippings at the Academy library that announced BLOOD OF THE WEREWOLF as an AIP title, not long before they made I WAS A TEENAGE WEREWOLF. However, Herman Cohen, the producer, claimed it was always called that. I don't think Cohen was lying; I think the error is a matter of timing.
We all know that AIP very often, probably most of the time, invented titles before they embarked on actually making the damned movie. Here's what I think happened: before handing the project to Cohen, Arkoff & Nicholson decided to make a werewolf movie and came up with the title BLOOD OF THE WEREWOLF, and the announcement was sent to the trades.

After that but >before Cohen was hired or a script was written<. Nicholson's kids read that issue of DIG with the (very) short story "I Was a Teenage Werewolf" and suggested it to their dad. (He always said he got the title from his kids.) THEN Cohen approached Cohen and Aben Kandel, who wrote the script--which >itself< was always called I WAS A TEENAGE WEREWOLF.
This is only a theory, but it seems to me to square with everything.