I wonder if the person who is taken off of the original PNR and given a new one does not automatically get the original time/date stamp? For example, if you bought 2 tix on one PNR on 10/15/2009 @ 8:15am, then called on 10/20/2009 @ 11:00am to separate the tickets, I bet one tix (original PNR) will still show 10/15/2009 @ 8:15am as the time stamp, but the new PNR will show 10/20/2009 @ 11:00am. In other words, if you are going to split reservations for upgradability, do it ASAP so you don't fall behind those buying their fare after you.

I seriously doubt the SMS reps can do much to change the 2nd tixs time stamp. Just a guess here, but it would be a logical explanation.