I have to admit to some surprise on some of the responses

I wanted a first class seat, so I bought a full Y with an immediate upgrade. These are the rules that CO sets - not me. On many occasions, when no Y upgrade was available I have purchased full first. On some occasions First is cheaper than full Y so I do that then also.

The equipment change was from an expanded first 737 to an unmodified - 4 fewer seats. If had been given a first class seat on the basis of EUA then I would have been unhappy but sucked it up, since I had not purchased a higher fare class in order to sit in the front. It is interesting to note that they did downgrade by fare paid - my seat still existed on the new aircraft but was issued to someone else: presumably a full fare F passenger.

WRT to going after the additional $50. This amount relates to the amount of compensation due according to the CO document given to me by the gate agent. She felt only authorized to issue $150, but the document she referred me to (and signed) clearly states that $200 was due.

I have not looked over terms of carriage, and she may have issued that document in error. Nevertheless, it was issued.