Yes -- "first and foremost" of those not represented there, is indeed 5ft. / 1520mm. There is a kind of "might-have-been" in this issue -- but wanting 5ft. as first candidate, I took steps to cut that one out. The Panama Railroad (parelleling, and much antedating, the Canal) was 5ft. gauge (inaugurated by U.S. interests in the 1850s: in the early decades of U.S. rail history, 5ft. gauge was quite popular in parts there, though it didn't last) -- Panama Railroad was 5ft., until converted to four-eight-and-a-half in 2000 -- 01. And Panama was part of Colombia until 1903: desirous, perhaps a bit meanly, of excluding P.R. and the 5ft., I took care in the framing geography-wise, of my question.
Senor, the next question is yours to set.