You really decided to wait from 9.45 to 16.05 to get a C-class seat on a 2 hour flight?
Many airlines (including QR - just visit the QR forum) have a policy to downgrade these on awards first. You are than still eligible for compensation. There is an Altea algorithm that determines upgrade/downgrade order (there is a thread on LH forum). I am not sure if TP uses this algorithm, but they are on Altea, so quire likely. As you were on different PNR's so that had no clue you travel together.
But as you voluntarily moved yourself to a later flight you are now (IMHO) not eligible for EU compensation.
1. In this instance it actually made little difference to us. I was arriving at destination very early one day ahead, getting there late afternoon did not bother me. Similar story for my wife. So while it is true that it was actually no big deal, it was the right opportunity not to get an airline to get away with inappropriate practices. Plus, there was not even a word of apology from the date agent, just "here is your now BP. You are now in economy."
2. That it may be policy does not make it right. Confirmed is supposed to be confirmed, otherwise it is for the airline to provide an alternative acceptable to us. As to compensation, would have probably be minimal.
3. One has to stand for principles. No matter that "many airlines do it," it's still wrong and a violation of the contract.
4. Our PNRs were cross-referenced.
5. We did not "voluntarily" move to another flight. We were very willing to stay on that flight as per our confirmed itinerary and in the confirmed class of service. The airline moved us to another flight because they were unwilling to provide the contractually agreed service.