I would not even make the effort to argue law (which always confuses me),
but base my statement about 1906 being the cut-off in the 1970s on my
experience with publishers and libraries.

In the late '70s I was writing a history of ragtime with *many* musical
examples, and was careful to ask for reprint permissions.  I was told
repeatedly by publishers that 1906 was the cut-off.  (Overwhelmingly,
most copyright holders gave permission to reprint a few measures of
post-1906 works without fee, also.  Very few asked for payment.)

Those of you who are old enough to remember (and not so old that you've
forgotten) might recall that in the '70s we were inundated with in-
expensive ragtime reprint folios that went up to 1906 -- because fees
had to be paid only on post-1906 works.

Ed Berlin