It wasn't uncommon to add a charger bridge to the older rifles after 1907.
The Military even adopted the CLLE (Charger Loading Lee Enfield), nothing more than the (Long) Lee Enfield with the charger bridge added.
I think you'll find in the BSA 1914 catalog reprint that the charger bridge on the sporters is offered as an option. Of course you loose the dust cover and the dust cover lugs on the bolt body.

The workmanship around the bridge looks a bit less than what I'd expect from a maker, but it is what it is and there's nothing that can't be cleaned up.
Perhaps it was ordered with a bridge originally,,someone removed the original at some point maybe for cosmetic reasons,,then one was re-installed at a later time.
I do notice that the butt stock has been cut for the operation of the No1 type left side safety lever.
That type not having been used on the earlier Sporters, perhaps the wood, though BSA marked was used on another rifle.