Rank speculation on why 201-212 instead of 200-211 -
Perhaps when the GP38s were ordered in 1973 the bicentennial value of the number 200 was already being contemplated, and the number deliberately left open to allow for the maximum flexibility in assigning it to a then undetermined engine...
as an aside, a number of years ago, before the model train manufacturers got good at applying every known paint scheme on every model, a small outfit called Bev-Bel did short run premium paint schemes of certain models. They did one in N scale of a B&M GP38 in as-delivered scheme. Which number do you suppose they chose,
212 of course. While interesting, as 212 only existed from 1973-1975, the number greatly limits the scenes that it can "rightly" be placed in !