Sooo much is/was left uncovered.
- Bristol, Napier and Wright aero engines
- Oerlikon and Solothurn weapons
- Soviet, French and Italian aero engines, from 1920s to 1940s (I'm talking about the much more detailed books than the ones available now, on English language and with proper proof-reading)
- racing/record-setting aircraft of the 1920s-1940s
- British tank engines
- complete history of DB/Mercedes aero engines, from ww1 to 1945, including the detailed account about the Japanese spin-offs
- Japanese engines on English language
- Japanese aircraft, not just the Zero
- Republic projects
- Japanese weapons for aircraft, especially the guns' firepower (a far more detailed account than what is written by Mikesh/Bradstreet and Williams)
I get it that some things will never be covered, like the Japanese stuff (a lot of docs was destroyed in Aug 1945), or the Republic designs (again a lot of docs was destroyed, this time when Republic was bough by Fairchild).