About Time in Grade (TIG) requirements

So I was just helping a friend of mine with some career advice (Idk why he asked me lol, maybe because I'm a new supervisor or something) and a good question came up for us regarding Time in Grade requirements and things like that.

Now, the way I understand it, is that since I started my career as a WG employee, and moved to the GS system, in order to apply to higher GS positions I need to meet the Time in Grade (TIG) requirement. But, what if the opposite happened? Basically, I'm wondering if someone were to go from GS to WG, would they still need to meet the Time in Grade (TIG) requirement for higher-level GS positions? I know their current TIG wouldn't go away (like, if they were GS7 for 4 years, it shouldn't reset just because they went to WG), but would they be able to apply for, say, a GS 11+ position because they're WG now and not part of the GS scale? OR would they only be able to apply for GS9 positions using TIG?

Thanks in advance for any help with this, I don't see anything from OPM regarding this stuff, so maybe some of y'all have an experience I could lean on to make sure I'm on the right track with my buddy.