No, not all of the H&H production is hand detachable. I wouldn't even hazard a guess at the %. All I can say is from my experience with them would be that a much higher % made after 1920 will have that lock feature as compared to those before 1920. And 1920 is just a breaking point that fits those that I have had over the years.

They were not specific to any one grade, but again from my experience a higher % of Royals and Deluxes will have the feature than the Dominion grade.

The locks were held in place by a thumb screw made in an "L" shape that went through the left lock and screwed into the righthand lock. If taken apart many, many times the inletting would be bound to wear somewhat. However, it had its advantages in taking care of the locks for preventive maintenance.

I hope that helps, Welcome too!