I don't think villagers call setPlacedBy when placing their crops either, though I suppose in that instance it wouldn't do anything.
An overflow could cause an error (as it is probably never intended), or Mojang could use an arbitrary precision format for the scoreboard so that there is no minimum or maximum.
I don't think villagers call setPlacedBy when placing their crops either, though I suppose in that instance it wouldn't do anything.