Wish I could answer that one. I see your point though, that's quite a drive. I guess your best bet is to trust him on this and expect there will be some variation from that which you looked at. Maybe emphasize to him how important it is to you, that it look like it's from the same batch, see if he flinches or shows any signs of doubt.
One thing to consider is that granite or any other natural material from the same supplier could possible vary from their own sample, as sometimes the sample could be a couple of years old and cut from a completely different batch of stone.