I thought the tags said standby (or at least, used to). It’s been several years, but that’s what I recall when on standby ex-Canada - where they needed PPBM, so bags only loaded once you cleared).

Again, in the past, there weren’t any special tags, at least for standby domestically, since bags aren’t required to be matched to pax onboard. At least as I remember, bags for standby were always tagged for the standby flight, whether or not the pax made it. Either way, they’d be at destination for pax to get.

I remember quite a few other trips with confirmed connections where bags traveled on earlier connections than me, sometimes even when I couldn’t book the connection because it was below MCT. I specifically remember this in fall 2011. I flew into DCA in the first (or maybe 2nd) week after it re-opened after 9/11, and surprised to find out it traveled on an ORD-DCA flight earlier than MCT and was waiting in the baggage office when I landed.