What you "know" isn't proof that we could take into court if we were challenged about it in 20 years, and the whole problem of "new copyright" [C.17] makes it effectively impossible to tell for sure what is and isn't copyrighted anyway, without reliable evidence like the title page.
You need to find a matching paper edition for proof. See the FAQ "I've found an eligible text elsewhere on the Net, but it's not in the PG archives. Can I just submit it to PG?" [V.62]