Jola
However, since my worse degrade (q200) was still more that +50 levels overcraft, I was expecting max exp on all crafts. However, I only got max exp on the undegraded q250 crafts.
Has it always worked this way? And if so, what is the benefit of overcrafting more than +50 levels?
yes, it's always (well, at least for the last 3 years or so that I've been doing it) been that way.
Crafting exp is reduced by a percentage (I think, might be a fixed amount) for degrades, the amount depending on the amount of degrading.
So if you would have got 5k at max oc without degrades, and had enough degrade to gain a 5% penalty, you'd end up with 5000-250 = 4750 exp.