So, what they’re actually doing for you is reticketing the reservation, waiving any change fees, to use native flight numbers instead of the codeshares. Often, LH and UA inventory matches, but it doesn’t have to — they’re allowed to be different, depending upon the specific agreements in place for how they’re codesharing that flgiht.

UA does have the ability to call LH and ask them to open inventory for you, and perhaps for a GS you might find someone willing to do it — but it’s still LH’s decision, and if they decline, there’s nothing UA can do.