Your are correct 1974 DT100 & DT125, when I was 15 years old I worked all summer saving for a DT100, spent many a nights looking at the brochure, when my mother took me to the local Yamaha dealer he didn't have a 100 in stock but he had a 125 that his wife had used as a demo, only had 150 miles on it and he sold it to me for the same price as a 100. These bikes were my "reentry" in to the world of motorcycles after a 25 year break. I found the DT125A in a barn in Kentucky, only had 3,200 original miles, the owner couldn't get it started, pretty rusty but all there. It was a total restoration job except the paint, it has a small dent in the right side of the gas tank but I love the fact that it has the original paint after 40 years. Its street legal, I run around Dublin OH in the nice weather, its a ton of fun and every single trip somebody stops me and talks about their old bike, or the brothers etc. plus at 60 mpg its cheap transport. The DT 100 just moved on to a new owner this week, I think I reached the "FAMILY" max for motorcycles 4 in the garage, 2 in the basement, and 1 in the office. So I was strongly encouraged to get rid of one, on the positive side it went to a great guy who want to teach his kids to ride and fix it up.
There's an even better story about the dealer that I bought it from.........
Tell us about those enduros. '74 125 and 100?