On the Sterlingworth you could not close the gun without moving the lever over to the right could you. If this gun cams the lever over, chances are it was never made with a latch. I currently have three doubles which never had a latch, one English, J P Clabrough, one German J P Sauer, & an early American Lefever Arms Co with the side pivot lever. All of these were designed to cam back the bolt upon closing & none ever had a latch. I have owned others in the past as well.
If you tried to close that Sterlingworth without holding over the lever you would have simply rammed the rib extension down atop the bolting finger & been unable to close it. That needed fixed, this one probably doesn't.