I've seen this happen on oversold flights. My friend booked a OOL-CBR last minute in economy, when he got to seat selection business popped up.
As for ATR, I'd avoid row 1 because it's the last passenger that gets off the flight (the doors are at the back), and it's far noisier (also more vibrations felt) in the front. The best seats reserved for Plat/Gold are the ones at the very back.