a (this parameter may be absent) — the sequence in which the members of a given class were ordered by CN. The first batch of locomotives of this type received are normally assigned "a", then "b" for the second batch, and so on.
GF-30c — Freight locomotive manufactured by GM, 3000 horsepower, third batch received (CN 5000 is an SD40 of this class).
MPA-18a — Cab unit for passenger use manufactured by MLW, 1800 horsepower, first batch received (CN 6760 is an FPA-4 of this class).
GR-412a — Four-axle road unit manufactured by GM, 1200 horsepower, first batch received (CN 1400 is a GMD1u of this class).
EF-640b — Six-axle freight unit manufactured by GE, 4000 horsepower, second batch received (CN 2430 is a Dash 8-40CM of this class).
GH-00a — Slug (no diesel engine, so zero horsepower) for hump service, built by GM, first batch received (CN 514 is a member of this class).