I have, and I thought this could affect it. But, for one Uranium ore patch I found and tagged, richness actually went down from 964k to 948k.
Most ore patches keep their richness as first discovered and are unchanged. So, the correlation doesn't make sense (to me at least).

Hi,

As I explore and reveal map, I like to place tags on ore patches with a number which represents ore richness. Example: "Iron 5.9M", so I can have an overview of nearby ore patches and their richness without having to hover with mouse over them.
Well, I noticed that after some time (not sure ...