You are correct.
Convertibles were equipped with "bolt in" style subframe connectors from the factory at Dearborn. However, the "weld in" style
aftermarket subframe connectors are far more superior than the factory SFCs (due to the better rigidity, etc). Additionally, full length subrames are "better" than the regular length subframes.
Definitely take a look underneath your car to see what you have - it's very possible the previous owner(s) may have removed the factory subframes and added aftermarket subframe connectors.