IIRC the very first run of the mk 11 was not serrated, the the later ones were, i have a '69 model i bought new in '69 and its serrated, IIRC they did make some non serrated ones with black handles, and some with camo handles in the mid to late '80s, what color is the handle on your knife?? i will look and see if i can find the addy to a web site that has all the mk 11 info ya would ever need ie manufacturing dates/variations/etc, used to have it on my PC till it crashed.
as far as rarity, i guess it might be a little more scarce than a std one but imho would be worth only a small premium, the really desirable ones are the viet nam era ones ie pre '72 or so, a bud had a set of matching mk 1, mk 11 and a guardian, mk 11 in this case not serrated all with camo handles, i think he still has them.