Sorry, but I was only able to answer your first question because I'd bought two 119 Specials in 2004, and one this year, so far. From looking at
http://www.buckknives.com/technical_making.php before 1986 Buck didn't use date stamps, so, I would presume that your 119 Special without a date stamp is from before 1986. However, your mention of the visible dowel may help someone in this forum, other than me, to help you to better determine the date. One other thing that may help you to date your older 119 Special is to mention whether there is one or two spacers in the aluminum of the guard and the butt. Older models have two spacers in both guard and butt, newer models have a single one in each.
I'd post this new question as a new thread, so that you have a better chance of someone "in the know," like a Buck representative, answering you. Definitely mention the 1/8" dowel in the butt cap, along with the number of spacers, fore and aft, and I think that someone can come up with a better answer than the guesses I'd be taking.
GeoThorn
(I remember seeing some pictures of a 119 Special with a "lanyard hole" put through the center of the base of the butt. I was wondering how that "lanyard hole" got there, since mine don't have them, and maybe someone just punched that 1/8" dowel out...?)