Mine are true to size.

for example:
Continental’s Sizing on 22mm ID rims
4Season 28mm: 27mm
GP4000 28mm: 31mm
GP5000 32mm: 33mm
4Season 32mm: 35mm.

Rim size does make a difference. I have some GP5000 28mms on 19c rims, and they are right at 28mm as I recall. I can't put the 28mm GP4000 on that bike, but the GP5000 works fine.