This is a standard India Pattern Bess which has at sometime during its working been cut to facilitate its fitting to a musket with a slightly larger barrel.  The modification is old as it is pitted commensurate with the overall aging of the bayonet.

While probably never an official modification,  it is just possible that it may be a field modification done under campaign requirements to replace a lost bayonet.  It does however illustrate the fact that two randomly picked bayonets of this period cannot be guaranteed to be interchangeable,  you must still rely on trial and error.