Originally Posted by Long Zhiren

Could you please explain that? Thanks.
I used to do it somewhat often at T-24.
This year, I tried to do it on several occasions and was told that I can no longer do it on the previous calendar day. Some leftover PMCO gate agents mistakenly thought that I could still do it, but on phoning into premier support line, was informed that this practice is no longer supported. PMUA agents don't seem cognizant of the practice. Because CO used to do it, security still routinely lets you through with a boarding pass for the next calendar day, to try to go stand-by on the present day's flights. But because it's not to be done anymore, it's getting clamped down on now.