The ANS library has 99 numismatic books published in 1927.
1927 wasn't a big year for numismatic works. The only book published in 1927 that I have read, and that was reprinted, is George Hill's Select Greek Coins. This work didn't become public domain today. It was published in the UK, and already became public domain in 2018 or 2019, 70 years after Hill's passing.
You won't find Select Greek Coins online. Google Books only knows it by the unauthorized 1974 reprint.