Well, there seems to be some conflicting information out there..
Extra 220 South, issue 77, from 1982, says both the GP9's and the GP18's had these numbers:
Old: DRS-3
New: ERSM-18
And they make no mention of ESM-18.
However, there are several photos that clearly show ESM-18 on the side of the GP9's..
So that is three different numbers in the mix..
Im pretty confidant that DRS-3 is the correct original number for both models..
the iffy part is ESM-18 or ERSM-18 for the later numbers..
photos say ESM-18, some printed rosters say ERSM-18.
(haven't seen ERSM-18 in a photo, but that doesn't mean they didn't exist..in the majority of photos you cant make it out clearly)
Perhaps they wore all three numbers at different times?
we know the numbers were changed twice..they could have been changed three times..
need better photos to straighten it all out..
Also, Extra 220 south did not include any dashes for any of the class numbers, for any LV diesels on their printed roster.
they listed them as DRS3 and ERSM18, with no dashes..
while the actual numbers on the side of LV locomotives always had the dashes, DRS-3 and ESM-18.
Since the locos themselves were lettered that way, we should probably consider the versions with dashes to be the correct nomenclature..
Scot