It wouldn't be the flooring contractor's fault that the subfloors between the two sections would be a tiny bit off. If the difference is a large amount, iit's the GC's issue. If it's a small amount, then it's likely within ''normal'' tolerances of difference between new and old.

It's virtually impossible to add on to a room and not notice that there is an addition. Sometimes you notice it right away, because the floor height may be different, or the ceiling may be different textures, or the walls may repeatedly crack between the new and old.

Even if they were perfect when new, the new construction will settle once it dries out. It will never be perfect, and even if it is in the beginning, it will not stay that way.

K- thanks for that. I guess my concern is that the new section will continue to settle (as it's only been a few weeks) and the difference will become very noticeable.