I never dealt with that on any of the Contenders I bought as complete carbines, but that was way back when TC sold them as such with 21" and 16.5" barrels. Later frames I bought were the same as the firstones I had bought, always as handguns. Never worried about it, still wouldn't, nobody you run into knows how they were first bought, nor cares as long as they are configured to appear legally when you are shooting/hunting with them or displaying them in public. No flags are being waved that some piddly law is being broken.
When I moved here where handguns are registered, all of the additional frames bought were as handgun frames which covered the bases if some LE ever did have a gripe. Never had one that did. Sold the ex carbine frames I switched long and short barrels on freely same as all my other frames until sold. I sold them as bare handgun frames through FFL's, effectively ending any doubt for the new owners.