In reply to Horacio Asborno's piece concerning date codes on piano
roll labels, I remember that some time ago Mike Montgomery and Ed
Sprankle (my best friend for many years, I still miss him terribly)
and I had a long discussion about this at Mike's house in Detroit.

Mike, an inveterate archivist of all things relating to piano rolls
and who is considered to be one of the world's leading authorities
on the subject, said that date codes did not necessarily signify
release dates.  They might have been the dates by which dealers could
return unsold rolls to the factory for a refund or credit.

Subsequently we all made extensive enquiries but apparently nobody
knows for sure.

John Farrell
http://homepages.tesco.net/~stridepiano/midifiles.htm