A couple of datapoints:
-BA is pretty notorious for overselling PE (and to an extent J) and cabin rolling to J / F if necessary (I used to get upgraded fairly frequently W to J or J to F when I was BA gold)
-On my last two trips to London flying back to JFK on AA105 (2:05p departure) on a Sunday (yesterday and a month ago on the Sunday after July 4th), flights were completely oversold in Y and W and cabin rolls occurred (I was on the upgrade list for an SWU anyways and cleared)

My guess on the second point (having worked in revenue management) is summer demand to Europe is much less premium and mix, and so my guess is that AA is more willing to oversell Y and W in the summer and op-up as required.

Can't speak for other markets (Asia or LatAM).