Well.. FWIW...
When I brought my 70 Coronet home from my parents house in 2001,
(it has been sitting in a garage since 1990) the original interior
was shot beyond all rational belief because mice had gotten in it!
When I removed the sill plates to replace the carpet, the carpet
was over the pinchweld on both the driver and passenger sides.
The sill plate was "pressed" on top of it to hold it in place.
I don't know if that's right or not but that's what I found.
I've owned the car since 1982. I'm only the 2nd owner and it was
definitely the original carpeting.
When I replaced it. The replacement carpeting (from ACC)
did not have enough material to reach over the pinchweld on either side! it did come right up to the inside edge...
But, the sill plate does not do a very good job of holding it down by itself.
So I sprayed alittle bit of the "spray adhesive" on the
floor board up where it approaches the pinchweld before
replacing the sill plate.
It looks good! ( a zillion percent improvement over what was left of the old one!)
But it was not installed exactly like the original.
The color and style (80/20 loop) matched great...