1936 Dollar

I always wondered how many AU-58 are actually circulated, and how many are MS coins with an accidental rub (like on the felt of an old display case)?

Is AU-58 something that people should understand as distinct from just better than AU-55?

There is much more than just a rub on this piece. You can see the contrast between the mint lustre in the devices compared to the dullness field on both sides.

IMO most AU-58 grade coins have actually circulated a bit. There are some uncirculated coins which have developed a rub while being stored in cabinet trays or paper envelopes ("cabinet friction"), but these will have full lustre and a slight rub on the highest points. There aren't many coins that are true cabinet friction sliders.