It depends on how efficient the brother handling territory is.
Some allow certain jws to keep their favorite territory for some time.
Some jws turn one in saying they worked it when they never got around to it
Some T servants try to give out the territory not worked the longest time ago (?) to certain publishers and they don't want it, "bad" neighborhood (too many black people), too far away, etc. So usually regular pioneers will take it because they want a "fresh" territory.
I remember one service elder would pick out the oldest ones and have a "campaign" of not knocking and just leaving a tract or an old magazine in the door so it would look like they were up to date when the CO came at the end of the month.