Interesting articles, Livestock-D
Keep in mind the USDA's list of "840" tags is almost a moot issue, since the "official tags" are a carry over from the NAIS days. However, some are still used in Scrapie and TB programs.
If you've had problems with Z Tags (or any other brand) when tagging young calves, here's a tip that will prevent torn ear ears. When tagging young or even "wet" calves, be sure to hold the ear taught when applying the tag. This will ensure you do not tear the thin tissue.
Here's another tagging tip card that shows where to place ear tags. This has worked pretty well for us.