If this thing contains explosives(not an empty shell) and it still hasn’t exploded, then explosives inside were relatevely stable(picric acid in contact with metal creates even more unstable compounds which can go off by themselves with time). If explosives inside are based on NH4NO3, then it is definitely stable also because of this salt is highly hygroscopic and looses sensitivity + power the wetter it gets. And I highly doubt that these grenades are actually sealed properly enough to fully stop contact with moisture(especially ones they became so rusty).
So, I think that this one definitely contains only stable explosives. But this doesn’t make grenade any safer and it is recommended to safely discharge by a professional in a prepared environment. Or at least to make sure that you are behind a thick tree/wall if you want to throw it inside a campfire by yourself.
Each instance has its own global set of rules. And then each separate community has its own rules. So if there is no rule 4 in community, then it is rule 4 of the whole instance.