Well, i usually find it is hard to say much about these at all. Dating them is generally difficult at best as keris sajen have been made over a rather large period of time without much in the way of stylistic changes dependent upon era. If i were pressed on this one i would say it is probably newer than your #2 sajen, but i couldn't say how much newer. It has less wear and cleaner lines for sure. It also seems to be trying to incorporate more ricikan of the modern keris into it as it seems to have a clearly developed pejetan/blumbangan. It also has a very clearly delineated gonjo line. You will find this on older sajen, but if Alan's collection is anything to judge by that incised line is more common on the alternative style with the handle that faces the gandik than on this more common form. Not that it never shows up on this style, but it could be an age indicator. Perhaps Alan has more to say on that.
http://www.kerisattosanaji.com/kerissajen.html