Just have to ask this question. Do you have a problem with old Assemblies losing their mates after you go to a newer version of solid works. Seems each year when we install the newest version I will have some mate break for one part. But that part is used in a few hundred Assemblies. So I have to go back and fix all of them. Usually find out when the shop floor calls and says the Assembly blew up. Normally this is caused because someone used a surface mate and not and Axis or plane.
Or if the Assembly had any locks in it this will also cause it. I have to go in delete the lock and mate it correctly.