In my opinion, sheet-music is incorrectly applied in most situations. I believe this is because the term is common to the general lexicon, and is applied by amateur or hobbyist musicians in places where it would not be applied by professionals, due to the fact that they have access to a larger domain-specific vocabulary (for example "notation", "engraving", "repertoire", etc.).
I think there are questions where this tag is appropriately used, for example:
In light of this, I don't believe we should co-opt the term to be a filter tag for western standard notation (already assumed to be the default if notation is present without any child tags like tablature). I would suggest instead that we limit the use of the sheet-music tag to where it is genuinely useful as above, and if we are in need of a filter tag for western standard notation, let's come up with something different that more clearly indicates as such.
Additionally, we would probably want to edit sheet-music's wiki excerpt to steer newcomers in the right direction of tags like notation, repertoire that they may be looking for in actuality.