Hi Rob,
I believe the L&R late flint has a fairly deep pan. As such, the lug on the bottom of the frizzen pan cover does not pack the priming powder down unless you put a lot in. Other than the lug siphoning water into your pan, it does no harm on that lock. That is not true for the L&R Queen Anne lock, which has a very shallow pan and the lug packs the priming down. Loose powder ignites and burns faster than powder that is packed tight. Most original late flintlocks have a notch filed under the pan cover adjacent to the vent hole. That prevents packing the priming in the pan at the vent. On any L&R locks I've used, I annealed the frizzens, ground off the "waterproof" lug and filed notches on the bottom of the pan cover. Then of coarse, I had to harden and temper the frizzen, which for my set up is easy to do.
dave