I have several sets and it seemed to me that they mostly do match up. Any mismatching can be solved by a little creating fudging. IIRC, in each set you have one tile that is meant to be cut apart to make tokens for furniture, ladders, corpses, stairs and such. Seems like there were also a few tiles meant to be cut into building sizes, rather than used as-is.
I'd have to drag those sets out again, don't use them much now that I have dwarven forge terrain. But I bet others here can confirm that those Rackham terrain tiles are quite well done and very useful.