I will hopefully soon be releasing "my" magnum opus, a piano transcription of the eclectic Quoniam from Missa Dei Patris (ZWV 19). As this is a simply fantastic work, dazzles on the keyboard and thereby sheds a completely new light on Zelenka's invention, I do hope it will be performed, even recorded (but not by me - it is too hard for me to play properly!). Before I release it I have some niggles about copyright. ZWV 19 was not published in the 18th Century and it seems that we generally assume it (along with its equally remarkable chums, ZWV 20 and ZWV 21) were not performed (my gut feeling tells me otherwise, but obviously I cannot prove anything!). If I understand copyright law correctly, this means that ZWV 19 is not automatically in the public domain. So, even though I only used the autograph manuscript (SLUB digital library) as source for my arrangement, I may be violating the copyright of the first person to publish ZWV 19. As far as I can tell, the first publication of ZWV 19 was in 1985 by Breitkopf & Härtel as an urtext edition as part of the series "Das Erbe deutscher Musik". That is 31 years ago.
Based on my very poor grasp of copyright law I believe that ZWV 19 is now in the public domain in the EU and I can safely release my arrangement without violating copyright of anyone. That is because, in the EU at least, Urtext editions (editions with very minor changes to the original manuscript) are protected for 30 years rather than the 70 years after the editor's death for non-urtext editions.
Are any of you more familiar with this type of issue and can confirm my interpretation is correct?