They don't get "digital" files or whatever from SNK/Aruze, they scan flyers and game artwork that's packaged with the MVS cart. I guess you could call that "getting them from SNK", but then anyone could get the "digital" files.
As for correct genre striping - that's an invention of a fan club, known as NeoGeoFreak.com, and is not Neo Geo/SNK/Aruze official. The stripes may match, look better, and categorize the games, but it's not official. It's one man's (or in this case NGF's), "opinion" on how the games should be categorized.
Unless it is a game that NGF produces, develops, and releases, then any touched up insert (or hand created) is by no means official or authentic. It would only be official for the games that they conceive and create, which has yet to happen.
How many times have you heard of someone (collector, whatever) touching up an antique only to degrade the value because it was no longer authentic? It looked nicer, but wasn't 100% original. The same is happening here, and people just don't see it (yet).
For unlreased games though, anything is fair game for home carts, but nothing is official or authentic since they were never brought to the consumer (home) market by SNK, and the consumer, collector, or casual gamer should not be mis-lead into believing they are authentic. The only true authentic form for these games are their MVS versions, which is what I prefer for the unreleased games. I do have some of these on home carts too, but they either have the FREE inserts/stickers/manuals, or none at all.
Don't get me wrong. The inserts (art, cart stickers, manuals, whatever) they create are very nice, and are obviously appreciated by many people. I'm sure they spend a great deal of time working on them. Personally, I like them (never said I didn't), but I won't use them (for released or un-released games). To me, how SNK created their inserts for they games they bgrought to the home market are the way they are supposed to be, errors or not.
Jeff