Date of first publication and derivative works

[flutist319]

This is a question about public domain as it applies to derivative works, not uploadability here, but maybe someone around here will know…

I'm based in the US. When I was young and clueless about copyright law, back in 2007 or so, I transcribed the fanfare from La Peri by Dukas for flute ensemble. (Though IMSLP was a thing back then, I wasn't aware of it -- I got a score out of my local university library.) Later, I learned that the piece was originally published after 1922, which would mean that my arrangement was technically illegal. So I thought: oh well, I just won't perform it in public until it enters the public domain. But then I looked it up again recently at http://imslp.org/wiki/Fanfare_pour_pr%C ... s%2C_Paul) and saw that a version of it was published in 1912. (I also notice that the usual "non-PD US" warning doesn't appear on the full score.) Could it be possible that the transcription was legal after all?