I'm surprised that there's no difference between a nonSchengen to nonSchengen transit (airside connection on one ticket) versus a transit where one would enter Schengen at AMS. In the latter case, there would be little to prevent someone without checked bags from simply leaving the airport and spending some time as a tourist in the Netherlands unless the authorities have recently installed some additional checkpoints (perhaps around customs). Maybe I don't understand where passengers' COVID-19 documents are being checked at AMS.