As others have said, advertised tire width is almost always different from actual tire width, at least partially due to rim width. I've found that most tires are narrower than advertised, a notable exception being Continental who generally runs true to size. I run Rene Herse Snoqualmie Pass tires on one bike, they're suppoed to be 44s but are more like 42s on the 23mm rims I'm using. Your experience seems to match my experience. Rene Herse/ Compass tires are awesome, don't worry about it and ride 'em.