A Spitfire/Mustang/Lancaster/B-17 etc census is relatively easy…The hard part is deciding what warrants being called a project as opposed to a box of parts dug up from a crash site. IIRC, last year a poster proclaimed the existence of a “new B-17 project”, but the news turned lukewarm when it was apparent that the collection of small parts was a long was from a project.

Also, some owners seem very reticent about their various remnants/projects/aircraft.
Why that is, I don’t know but in the hobby there are secretive owners and their friends who like to play the “I know something you don’t know” schoolyard game.

Another problem is keeping track of preserved examples of more common or newer “warbird” types, many of which are still being scrapped as collections close…or types in wide use and are wrecked in private use.