when i made the booking, i asked them to specifically state on the phone that we are confirmed for all segments. and i made her repeat it clearly. (prophetic?) so there is a recording somewhere, of a united agent confirming our seats.
It was confirmed then, SN made all changes later (talking what I saw from my PNRs & others - I didn't see yours) and no action was taken then
Comp IME needs to be paid by SN - they made all the changes and the mess