The problem with the model year is pretty obvious... You see, the model year since the mid sixties began in august, so it isn't strange if it's registered as 1968, since it was made in december 1967. I myself own an economy bug , made on july 1967(still with sloped eyes, 6volt....), and the chasis number says pretty much too. The first two digits name the type(model) say 11..., the third gives us the year example 117...(in your case it should be 118)And the rest of the numbers might help dating approximately.
Sorry about the grammar, i got a little rusty, since i haven't spoke, or written in english for a few years.
i've seen some historical articles on www.vw-resource.com
Davor, Serbia