jbfield, I hardly see your situation as unusual. Before ASR was paid, this happened regularly that a preassigned seat was changed when the configuration was changed. There was never a guarantee that you will get a similar seat back. There was even a thread here when we were discussing how far behind the curtain one should take a seat to still seat reasonably close to front, but not risk reconfiguration...

PS1. it is annoying that they would give a middle seat to *G. I do not think that the staff is very considerate here.

PS2. There was not any ASR for *G on SK, as far as I remember.