I suppose I should start monitoring this group since I have some interest in the rules....
After the cue ball contacts an object ball, some ball must make rail contact. Rail contact is defined as a ball that is not touching a rail and later touches a rail.
A ball that is frozen to the rail and is simply driven into that rail does not make contact with the rail.
If a ball is frozen to the rail, and a ball hits it straight into the rail, some argue that maybe the frozen object ball rebounds back into the ball that and then goes back to the rail, so that it left the rail and returned. High speed video shows that this does not happen. The object ball is still in the rail when it contacts the cue ball the second time.
And to be complete, I'll point out a corner case. It is unlikely that anyone here will ever see this shot, but it is possible. With a soft, close masse on a frozen ball, it is possible to get the object ball to double kiss, move a little off the rail and then have the cue ball reverse direction with the masse and knock the object ball back to the rail. If you plan to play such a shot, you better explain what you're going to do to the ref before you shoot.
Some rule sets go on to cover details if the frozen ball leaves the cushion and returns to the same cushion for the cushion contact. The WPA rules allow such a return and do not specify a cause. The CSI/BCAPL rules state that the ball must strike an object ball before it returns to the same rail. That would disallow the masse shot in the previous paragraph. If a ball that was frozen is moving nearly parallel to the rail and rolls back to the cushion (unlevel table or rail groove) the WPA rules allow such a contact to count but the BCAPL does not.
If a ball is frozen to the point of a side pocket and it is driven off that point to the other point, some rules sets do not give credit for the rail contact because it is the same rail. The BCAPL does give credit because it talks about cushions and there are six cushions -- two along each side rail.