For Myanmar, having "De facto independent areas (e.g. Wa state)" at admin_level=3 is wildly ambitious, since not only are these boundaries constantly shifting slightly due to the ongoing civil war, the actors involved don't even necessarily have the state capacity to accurately demarcate their own territorial claims.
The Wa State in particular appears to have undergone some "boundary fixing" a few weeks ago https://www.openstreetmap.org/relation/9399863 but whether it now accurately reflects realities on the ground is anyone's guess. I'm inclined to believe the Wikimedia map https://commons.wikimedia.org/wiki/File:Myanmar_civil_war.sv... showing Tangyan in Wa State territory is more up-to-date, unless they withdrew for some reason without it making the news. (The most recent I could find is this article from March where they were mining quartz in the area: https://english.shannews.org/archives/29385 )
Documenting disputed borders or borders in war zones seems tricky in general. Not only can they be constantly shifting, but even at a fixed point in time, the boundary is probably wildly different depending on which of the belligerent parties you may ask - or in extreme cases, a party may deny the demarcation exists at all.
Disputes are not such a big problem, since you can have multiple independent versions of the boundary with claimed_by= and disputed_by= tags differentiating them. But you do need to find out somehow where the claimed boundary even is. Like, does the Wa State have an Office of Cartography where you can ask for the latest official maps? I haven't looked super hard, but I doubt it exists.