DD,
I updated the production dates for the 4516.
Thread "4516 vs. 4516-1 vs. 4516-2" states a dual recoil spring for the no-dash, so I've changed the comment to "may have single or dual recoil spring" to cover both instances. Your historically letter wouldn't happen to have production numbers would it?

GH,
Added the CHP 4006; while its features are not really that unique, it is listed as a separate model in the S&W parts list.

Now if someone can tell me what the heck a M5946RCMP is?