A box may not already exist labeled "bluegrass". Usually one does, so I don't know why it would even be an issue, but if it didn't--well, it's not country, it's not rock, it's not blues, but it's definitely very representative of a regional culture of a given country. (As opposed to fusion, which is what you would get if, say, you played "Whiskey Before Breakfast" on a Chinese pipa, where tune and instrument are otherwise utterly foreign to one another.)

And "crossover" is by no means bad or new. Crossover has been happening for centuries and is part of the development of a musical identity.

My brother recently got into Cuban music, which would almost certainly fall into World unless you live in an area with a heavy Latino population that has a separate Latin section (Texas often does, but I'm sure other places don't). It's not necessarily old music, either, but it's very much Cuban.

I've even seen Cajun in the World section, which is both weird and sort of obvious. It's regional here, but it's pretty foreign even to most of the U.S.





The other option would be to ask the guy at the counter where they stock the [whatever you're looking for]. Personally, I've never had trouble finding what I want in a record shop because of ambiguous classifications because most things aren't going to be "eligible" for more than a handful of categories. Some places put Norman Blake in bluegrass, some in country, some in Americana, and some in other (next to World), and those categories are normally located near each other because of the potential for overlap.