To be honest very small. If economy is overbooked on your flight and there are not enough people entitled to a last minute upgrade (only S, Y, M classes) then they may OpUp some people but they will normally choose TPL, PL, GL, SL first and only then regular Matmid members.

So I would not hold up your hopes.

That said, you were very lucky to get 2 OpUps with LH so who knows - maybe luck follows you