A few of the George Granger sidelocks have a system where the trigger for the lock is pushed forward, and the lock is released, and pops up at the rear to be removed.
I saw a gun built on this system in the mid 1990s, when I was at the shop. There is nothing external and no way to see if it is a removable sidelock.
I have no idea when the company started using that system. I have also seen Grangers with the more typical small lever.

Best,
Ted