Now that I think about it, you are correct. The lanyard hole was simply smaller on the earliest "Paramedic" models, but the steel was indeed stamped "SPYDERCO-USA". As were the earliest Worker models, I don't believe this was ever true on any other model besides these two. See
http://www.spydiewiki.com/index.php?title=Image
aramedic_rh.jpg for a picture of an early Paramedic. There were also differences in the scale thickness (and potentially even the blade steel, though all the early ones were unmarked). I believe this would be enough to qualify for an actual variant, at least in my book.
I don't recall the exact story about why the marking was eventually changed to just "SPYDERCO", but roughly I think it had something to do with the knives being made in Japan, but Spyderco was a USA company. I don't think the rules in the US allow this type of marking unless the product is made here.