4506517,
I believe you are correct. On the later TSW models, S&W used the same slide and frame on both TDA and DAO models. On DAO models, they installed a "firing pin retainer" into the cavity machined for the manual safety body and substituted a DAO trigger and hammer. The good news is they can be converted to TDA by changing a few parts. A much more modular and convertible design but a heavier double action pull.
John