I created a custom world, where I set Iron Ore spawn size to 36 (default is 9) and spawn tries to 5 (default is 20). My expectation was that iron ore would show up less often, but in larger groups, so it would balance out.

Instead, I'm regularly finding veins that are way larger than 36. I just found one that was 114 total. At first I figured that ore veins sometimes clump together, but I think this way beyond that.

I use iron as an example, but I see the same thing with other ores. I set Coal to size 50 with 7 spawn count. I just dug 230 out of one vein, and I stopped mining because I didn't see an end to it.