But the most compelling evidence is that data plate. The serial number is 4529. By the time Amberola manufacture reached that number, the factory was 1000 units into 1B production. (The August 29, 1911 date on the data plate also rules out a 1A.) Yet it's HIGHLY unlikely that this early 1910 Pooley cabinet - desperately needed by Edison at the time - was fitted with a 1B mechanism in 1911 - 1912. Far more likely that when this 1A was modified, a blank (non-serialized) 1B data plate was pressed into service with a sequential number for a B 250 Disc Phonograph, and the "B1" marking was overstamped with the B 250 designation - perhaps by hand. My point is that this data plate is NOT original to the cabinet, since it originally housed a 1A mechanism.
Who would have had a blank data plate, gone to all the trouble of effacing the Amberola decal and substituting a later one, refinishing the lid, and even modifying the motorboard braces - - other than the factory?
I'm certainly not suggesting that I know the story behind this machine (I can't explain the post-1917 motor plate). But considering the other similar known examples and the existence of the data plate with its inherent logic, the possibility of this being a factory modification should not be dismissed out of hand - despite the carelessness with which it was done.
Just my opinion!

George P.