Not "really" tag related but...in art there are times a character without context or dialog is in the middle of an "undressed state" but because of some pose and/or state of the clothing you don't know if they are...wearing or undressing self, for example holding a white sock on their feet but legwear aren't like not nearly out (undressing) or stretched (finishing wearing it).

Is there really a name for an ambiguous "undressing/dressing" self or something? Or I am overthinking too much?

There really isn't a name for ambiguously-one-of-these-two-states for that one. But there are a lot that can be ambiguous, for sure.

I think most people default to use undressing if there's no clear indication that it's actually dressing. Since it is the bigger tag and often the default assumption is undressing-is-prob-happening, so for searches that works pretty well. And "dressing" is saved for when there's indicators that it's actually happening in the other direction for once. Which is useful, because it's the exception to the default expectation. Hopefully that makes sense.

So I'd say that if you really can't tell which way it is going... then lean it slightly towards "undressing" when tagging it.

there is partially_clothed, referring to a character whose clothes are in a partial state of "on-ness" which could refer to either situation.