I've encountered the supplemental page thing mostly in Schengen countries to the north or west of Germany, but I also had less use for transiting Germany on trips from/to the US in recent years pre-pandemic than going via CPH, ARN, OSL and AMS.

Let's see how many years it will be until using the current general circulation stock for ordinary US passports increase the risk of some additional scrutiny because passport control assumes that the "older" stock should no longer be around and/or isn't legitimately valid. This kind of thing used to happen at times with some people who were on the tail years of validity for the green cover US passports.