A couple things:

The C-12 time can't translate to a type because the airplane weighed 12,500 lbs. When the BE-300/350 came along they were over 13,000 and hence the type rating.

I got my ATP at an ATP school, but I got my DC-9 type rating with my NATOPS jacket and logbooks at the FSDO. Same with my CV-580 and BV-107 types. When I upgraded on the MD-80, the FAA had done away with Commercial type ratings so all mine were automatically upgraded to ATP types.