Did the late 70s to early 80s have thicker shift cables? It seems the smaller shift cables of today can more easily slip through the pinch bolt. I've got an old suntour VX front derailleur and that pinch bolt will not clamp the cable in the indent on the casting where its supposed to go. The nut is plenty tight against the flat plate that holds the cable. IT slips when you pull the shift lever a few times. (suntour downtube ratcheting power shifters)

Are there different size shift cables and can you still get the larger ones for older bikes?
I know ive taken what appeared to be larger diameter cables off on older bikes but perhaps they were just coarser wound so they looked bigger. Todays cable strands are so fine it might just be an optical illusion.