Besson Fridays at Home, Episode 2 | Besson Brass

Second episode of Besson's new webserie "Besson Fridays at Home", hosted by our artists Philip Harper, Steven Mead, Roger Webster and with special guests Sheona White and Mark Wilkinson.
The next episode will be livestreamed on our Besson facebook page, on July 17th. Stay tuned!
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[@danieloleary1782]

I am having difficulty finding an answer to what should be a simple question.
What defines an A model Besson Cornet from other models ? How might an A model differ from other models regards bore size , quality, etc.?
As I write I am awaiting delivery of a silver plated london made A model Bd Cornet with an A key lead pipe included. Apparently manufactured in the mid 40's, serial number 133522.