A recent example for me
WasRecentlyDamagedByCreep() works for hero. Does not work for any type of creep
GetAttackTarget() works for hero and lane creeps, however does not work for neutral creeps.
For me, the main issue isn't them not working.
It's that there is no documentation on what they apply to.
Combined with unimplemented unit scoped functions simply returning nil, which in many cases is also a valid return value for when the function IS implemented.
This means you have things silently failing, which are generally hard to debug
It would be nice to have at least one of the following
1) All unit scoped functions implemented for all unit types
2) Documentation on which are not implemented
3) an exception is raised when an unimplemented unit scoped function is called, rather than returning nil