CN S.A its just a different compilation and those are maps you can buy at garmin website.
City Navigator Argentina.. doesnt come in MS format, img only and you cant buy it at garmin website. You can only get it if you have nuvi 44, 54, 57, 67, 2497, 2597, 2797 purchased in argentina, paraguay or uruguay, since it comes embedded at those units only.
The coverage its a Little bit different between CN.SA and City Navigator Argentina.
City Navigator Argentina coverage its close to Mapear free maps coverage, cause Mapear provides information to Garmin, so they build the map based on that information