Going off of only FunctionID will either have a lot of false positives or false negatives, depending on if you compute them masking out operands or not. If you mask out operands, then it says that "*param_1 = 4" and "*param_1 = 123" are the same hash. If you don't mask out operands, then it says that nearly all functions are different because your call displacements have shifted due to different code layout. That's why the built-in Version Tracker tool uses hashes for only one of the heuristics, and has other correlation heuristics to apply as well in addition.