Carton (i.e. like SNES, "cardboard") boxes were used for many Japanese release games (though all also got a plastic box release). Not surprisingly, they can be worth more when the box is in good enough condition (Neo-Geo.com lists games at about 3x price for a "high" condition cart box as they would for one in "low" condition), but not as much as you might expect - this style of release might not have been all that uncommon at first. They look good, too - the top, bottom, and sides are printed with a solid color (black for Nam-1975, red for Sengoku) and the game's title logo.
Both Nam-1975 and Sengoku have shown up recently in the carton box, whereas I haven't seen either as plastic releases. So, anybody comments on this?