6-12065 is a remote control switch with no command control capability. It only operates with the remote control. It cannot be thrown via the TMCC /Legacy handheld.
I believe 6-16831, and 6-81949 are essentially the same. Both are remote controlled switches that have the option of command control capability, meaning they can be programmed to activate with the TMCC/Legacy handheld.
The 16831 was the original run, the 81949 is the newer run with an updated part # and its possible some of the electronics may have been changed or updated due to component obsolescense and/or improvements.