All Pentium IIs are clock limited. The multiplier they are supposed to run at is the maximum they will handle....ie a P2-300 has a multiplier of 4.5 and will only operate at a maximum of 4.5.
Some P2s are clock locked as opposed to clock limited. Clock locked means that they can only run at one multiplier, and not lower ones like those that are clock limited.
P2s that are clock locked are all manufactured after August 1998. That means usually 350 and above.