The CC search function limits searches to the last two years and it’s unlikely one has happened in that time but I am
pretty sure one was reported in the last 20 years. You are very unlikely to hear about it since the customer takes the offer from RCI and is happy to be bumped with the compensation offered. We are not talking about involuntary bumping.
While even less of a chance, you could get bumped even in an assigned cabin. Most of the time it’s not due to overbooking but some unique issue on the ship which removes some cabins from inventory.