It would be interesting to see a combined list taking into account both US "1930 or older" rule and more common internationally "life+70" rule, to see what works have finally escaped both of those and make works a bit less unsafe to make use of, but I have not seen any list like that?

If you have a list of life+70 works, filtering that for works released before 1931 is pretty straight forward

The more difficult part of any such list is the editorial decision which works to include. Even if we only cared about books published in English that would be thousands of books each year

That sounds like a good project for you then