I can provide a couple of possible answers. I've been working on an updated vendor list for the Mitsubishi and Satoh tractors that will provide much of this. A D prefix (example: D1600) is a tractor built primarily for the Japanese domestic market. Don't know if D = "domestic", but it's convenient to remember. These will always be grey-market units. (A D suffix means 4wd.) MT simply means Mitsubishi Tractor. Greys and US-spec models used this prefix. Satoh tractors had an S prefix that was changed to MT after Mitsubishi took over Satoh in 1980. Suzue greys had an M prefix. MTE is a Mitsubishi unit and seems to indicate a later version of the equivalent model without the E. The first two numbers on greys indicates the hp rating, which is always a PTO rating on greys. Example: MT1801 is 18 hp. That's enough for now, but it's a start.