it's more likely that A.C. 12.109 is the plate description (plate number etc.), not the opus number/catalog number. It refers to publisher's plates. (and is helpful for figuring out publishing dates sometimes- for example there's a table of plate numbers at Choudens.) Thanks for contributing, it's interesting to have works like this (I've uploaded some here from other sites myself...) Eric 18:27, 11 March 2011 (UTC)
