The fuel cap on the 425/413/426 used to be at the end of the tank, pre-1975 or so. Apparently enough people were opening the cap to refill while the stove was still running or hot that they redesigned the tank so the cap was on the inside, requiring you to completely remove the tank to refill, hopefully preventing people from spilling fuel on the hot burner.
I suspect there’s a similar story with the fuel cap lanyard.
