It was part of the orig message when the Sig's started coming on-line. Operational units were not to maintain both weapons on hand at the same time, and indivals were to be qualified in one or the other, not both. The only exceptions were SAI's that supported multiple units with differing weapons.
This was all years ago, there shouldn't be any units out there still trying to transition.
The SAI exception may still be in place if you have a PSU in your AOR, but other than thet it's one or the other.
In the beginning HQ & TYCOMS had to set forth policy to expedite the change out of PDWs. This task is almost complete. Units were not to have more than one type of PDW. The same could be said about any weapon that was used for the same purpose. There will always be a “transition” period which eventually comes to an end. But to answer the question YES, if you are an SAI and have to instruct units in your AOR then you are expected to have both qualifications. SAIs are at the disposal of the Armory Det Supervisor (District back in the day). Again, only if you are expected to train others. If you are solely utilized to train your unit personnel then you only have to be qualified on what you are outfitted with.
I have seen many posts on Fred’s Place asking about policy. The best thing to do and the official thing to do is to contact your Servicing Armory. If they need further guidance they will contact AREA, and so forth.
