When labeling individual wires be sure to place the number far enough down the wire so that when you crimp on the terminal you have the space. I usually crimp the terminal then slide the clear back up the wire and melt both the terminals heat shrink and the number shrink together.
While the IDEAL numbers are fairly durable the addition of clear heat shrink takes it to the next level of durability. Some owners will be happy with just the numbers and some are willing to pay for the clear heat shrink step. As a DIY I'd suggest going over the IDEAL numbers with clear shrink..