Good lesson and great outcome for OP. I think when you get signs there is a risk you might not fly in the cabin you purchased, it is a really good idea to be proactive. If you wait until nearer to travel date, there may be no good options left to move to. I think the airlines who try to solicit volunteers tend to be in “let’s make a deal” mode and as OP found out, willing to both give you assurance by putting you on another flight and putting some $$ in your pocket.