You'd think the Dash-9's would have many phases, they've built thousands of them over something like 11 or 12 years! I know that there are three basic types on CN:
Type 1: CN four piece windshield "comfort cab" (BC Rail also has 4 of these, and with CN's 23, only 27 units of this type exist)
Type 2: GE North American cab with "teardrop" or five sided two piece windshield
Type 3: Same as Type 2 but they have air conditioners under the cab
I bet Robbman could list more, but these would be the most noticable spotting features trackside. BTW, do these differences even count as phases?