NS's 9990's

A while back I saw NS# 9992 on a Dash9 and I saw on a roster they only went up to #9978. I thought I must have misread the number but then I saw a picture of #9997. So why did NS change these numbers? http://www.rrpicturearchives.net/showPicture.aspx?id=455129 (the third unit).

The second unit in this picture is 8997, from the same angle if you want to compare them.

http://www.rrpicturearchives.net/showPicture.aspx?id=377093

OK, the one I saw must have been 8992. I guess?

You might have seen a 9992. I’m just suggesting an alternative.

Not sure about that picture,I couldn’t really make out the number,
but my 2006 roster gives 9977 - 9999 (23) as as ES40DCs.
So according to that,you could have seen 9992.
(not sure why that picture is labled CW40-9 though.)

Which roster do you use?