Recently purchased a "1980" DT100. Bike needs some work, but the important bits (engine, transmission, and carb) seem to be in great shape. Thing is, as I dug into it, I noticed it has points, not a CDI system, as well as some other differences. I used some of the VIN charts here and the mystery deepened. 

Bike has a VIN of IT9-070801, which, at first glance, because of the IT9 prefix, means it's actually a 1977 DT100D. Thing is though, according to the USA VIN charts the VIN range for 1977 stops at IT9-017690. However, the 1958-2010 Yamaha Model Index shows the 1T9 VIN prefix being made from 1977-1983?
Also my bike is clearly red and not the yellow for that year.

I'm in Canada, but I thought we mostly got the same bikes as the USA. Did Yamaha just sell the 1977 DT100D for five years here with few changes? 

 from near Salisbury, UK.

Your VIN fits into the 1980 tables that you made reference to, so that sounds fine.

I guess that the models that the US and Canada got may have diverged at some point. Either that, or someone has replaced the cdi with points? A little more Canadian research needed here!