I was moved once from an ANC to SEA flight. Ended up in the middle exit row (was in 6C). I had picked the seat about six weeks or so pre flight not even thinking about it.

The day of the flight someone requested it. Technically, and I cannot confirm this, I believe a formal request is supposed to be made at least 48 hours in advance to get the seat if your needing it due to a disability. The person was blind and what could I do. I got called up (thinking I got an UG, awkward....) and told I was moved as was the person who picked the one next to me. She ended up further back.

So now, I don't chance it. 1. it's not good carma, if someone needs it, then I assume they will pick it. 2. I like knowing I won't get booted, not a gambler.