Late jumping in here, I just joined: Sorry to hear about your dad.
We use the smaller tags at first for our calves AND color code them. (Pink and Blue) We also use a paint pen to write the moma's number on the front and back of the calf tag. That way you can read it coming and going, just like all the moma cows. IF they are keepers, we change the tag our to a larger one. I have been thinking of adding the birth date to calf tag - just for faster reference in the field. I am thinking as I walk around checking the herd I can compare them with each other as they grow without have to reference back. We have a small herd, so I like to take notes and see if there are any patterns. This helps to know also if a cow lets other babies nurse - in case I need her to nurse a orphan.