Curious on what happened on my recent flights, ORD/LGA.

I am 1k, traveling with my three minor children (no status). I applied PP for both directions (waitlisted) (I have 2x 14 year olds, and 1 10 year old). I hadn't realized that it would auto-split the PNR when instruments were applied (leaving all of my minor children on different PNRs from me... whoops! Thankfully, it didn't cause any issues other than the minor inconvenience of having to check them in manually at the airport), and so on check-in, I got split off and upgraded. I let one of the 14 year olds take the seat (they are quiet and mature, and knew they'd be fine on their own for the short flight). Just before boarding, another seat came available - they split off my 10 year old's ticket at that time (and the 2nd 14 year old took the actual seat, leaving me + 10 year old sitting together in economy).

So now, on my return trip, we had three PNRs - my original (which now had only my two 14 year olds listed), my new one, and my 10 year old's new one). We still had PP wait-listed for the return flight - and on check-in, we were #1-4 on the list... what surprised me was that I was #3! (We were offered at the very last (already seated) second a single upgrade - to one of my non-status twins, but we turned it down. You're welcome #5 LOL)

Ultimately, it wasn't an issue, I'm just curious why I didn't end up higher than my original reservation?