They came with those plates and it looks factory correct. However, I make very accurate reproductions of that plate so its possible somebody recently added it. You'll need to study the raw metal for signs of recent activity to figure out what you have. My reproductions are sold in bare stamped steel. Here is an original side by side with mine. Its important to note these varied from the factory, one version had a flattened area where they bend, and one was a smoother radius there. There is no rhyme or reason as to year or model, it was random as to which car got which one.

The picture showing the plate welded in place is a section of original floor pan with the factory plate in place. It shows the factory welds which were short wire welds spaced apart (not a long continuous weld).