Hallo Sally
Please put this up on concertina dot net with a photo.There are a number of concertina historians on there who will pinpoint this concertina for you.
There were a few Music Hall acts that played a split concertinas similar (I think to what you refer to)Where the player plays the concertina normally for part of the act then splits the two ends apart and plays the two (one in each hand) as a duet.
My memory fails me as to whom the player or players were., but someone will know a names or names of the possible player of your concertina.
Very interesting posting.
Al