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 got an end pillar that spawned on top of another end pillar!
The top pillar encased the lower pillar's crystal with obsidian!
I don't think villagers call setPlacedBy when placing their crops either, though I suppose in that instance it wouldn't do anything.