From Fatal Fury 3 (May 1995 - first snap-lock case game) to early 1996, the snap-lock case has mat finish.
Pro - very scratch resistant.
Con - as soon as it ages, the surface begins to curl up, not only is this cosmetically unappealing, it's also creating wrinkles on the inserts. All of NGDEV's games come with this type of snap-lock case.
Starting from mid 1996 (the first one I saw is Neo Turfmasters in US), SNK switched to shiny/acrylic covers. In Japan I believe some games still had the opaque/mat finish snap-lock case up until mid-1996. My Ninja Masters came in with this type.