The licensing of the basic Bell-Tainter patents to the American
Graphophone Co. (from Volta Graphophone Co) occurred on May 15, 1887, as good a date
as any I suppose.
It is even possible that some Type A Treadle Graphophones were made
that same year (1887), using ozocerite cylinders (on cardboard sleeves).
In a message dated 11/15/2012 6:13:23 P.M. Eastern Standard Time,
[log in to unmask] writes:
Wilentz says book is using 1887 (hence 125 years in 2012) as the formation
of the American Graphophone Corporation.