Emerald, Iron and coal ores can be found above its supposed max generation height

The bug

Don't know if this is WAI, but I'm basing this report on the image that Mojang provided about ore generation, which shows that iron, emerald and coal ores generate up until Y=256. But upon testing, these ores can be found way above this number.

How to reproduce

1. Create an Amplified world
2. Run: /locatebiome minecraft:mountains and teleport to them
3. Upon exploring a little bit, you'll see that some ores generated in Y=280 or similar