I forgot to mention, if inf is off, it may affect close focus as well..
At inf, the focusing lens elements should be at the closest point relative to focus plane.. When u focus for something close like 8 inches, the focusing elements on the other hand will be at its farthest point relative to focus plane.
The real life effect maybe that a lens which is supposed to focus at 8 inches, can only focus at 2 ft for example if inf focus was way off. If inf focus was pretty close, the affect on close focus may not be that bad.
Most of the cheaper third party adapters and some of medium price ones as well, due to leeway in acceptable manufacturing tolorences, in the past have targeted nominal case to be slightly ahead of real inf point, so that something slightly over tolerences will work.
Amazon's Fotodiox line for example has to lines, the normal cheap one and the pro line... Where I suspect they are using better tolerences or they are simply cherry picking off the manufacturing line the ones w/ the better tolerences.
So far the only adapter I have never had to play inf adjust is the novoflex. Even the more expensive Fuji m adapter is ever so slightly ahead of inf focus point. I have had to shim all the third party adapters I have ever bought except a fotodiox pro one.. The Fuji and fotodiox pro ended up close enough it was not worth the trouble to take it apart and shim.
Gary