The rolls will be crimped. They will look like any other roll in the box. However, they will be full of the same date. This is my assumption of how it happens
1) Who ever is rolling the coins (armored carrier, coin service) runs out of halves and places order with FED.
2) Bags of old and new coin (1999-2001) gets delivered to carrier. If the bag is new it will be of the same year and mintmark.
3) Bags are poured into roller
4) If the new coins are placed in first the first boxes will be all the same date.
5) If the new coins are placed in the middle or top it is possible to get a few solid rolls. You have to crack a few from the box to make sure there isn't any older coins mixed in.
Again this is my guess. If you have a choice I always save Head/Tail rolls versus Head/Head or Tail/Tail