Hello, there, and welcome to OSM! Thanks for cleaning up and normalizing tags on boundary relations. Some of these relations haven't been touched in many years.

By default, though, we expand abbreviations unless the abbreviated form can be argued as "more proper" (e.g. brand names, surnames, etc.). In this case, "Ste." is an abbreviated form of "Sainte", and the first sentence of the Wikipedia article you refer to even uses this expanded form.

I think we should spell it out again as "Sainte Genevieve County".

There's a wiki page on this: https://wiki.openstreetmap.org/wiki/Abbreviations