I have removed a ton of staples in the last several weeks to gain access to the nuts on the bolts for deck gear. I have found at least two or three distinct sizes of factory staples. There is a smaller-wire, about 5/16 or 1/2 wide, and a narrower heavier gauge wire that is driven deeper and is harder to extract. Then, there are the narrow ones that you seem to have found.
Since all were probably air-driven, they must have had multiple guns shared around when installing the vinyl headliner. Those original staples have rusted over the decades, too. For restoring the perimeter of the headliner, I may have to buy a small compressor and gun to drive several sizes. (my old hand-operated stapler works fine on soft woods, but balks at harder stuff.