Yeah, it's definitely not super clear cut. I would have gone with the definition https://wiki.openstreetmap.org/wiki/IT:CAI#Percorsi_escursionistici, which uses the following description for `rwn`: _itinerari di lunga percorrenza che attraversano più province e/o mettono in collegamento più percorsi ordinari._ I think the 500 trail fits all these requirements.

Yes, there is not really a network of such "medium distance" trails in Italy, but I don't think it should be an argument against using the tag value, as these routes still connect to local and national routes in many places. IMHO `rwn` could provide a good distinction between short "single day" and longer "multi day" routes (that aren't quite of the caliber of the super-long distance routes of say, the SI or E5 for example).

I hiked the 133 (Sentiero Aldo Bonacossa) last summer. I wasn't so sure how to tag that one: It definitely is a multi-day route, but the paths are in parts really narrow (in some sections even pathless) and the route is in large parts only rarely traveled. But given that the route is quite prominently signposted at the start/endpoints, I'd now tend towards also tagging it as a `rwn`. Similarly, the same applies also to the few longer routes of the AVS like the nearby https://www.openstreetmap.org/relation/5487056. PS: Another nearby hiking route of similar distance which already has rwn is https://www.openstreetmap.org/relation/11009657