OP: Four digit numbers outside of the 2xxx range could indicate extra trains. For example, the Ski Trains out of Denver are 1xxx series. I believe Amtrak California has a couple 1xxx that pop up occasionally.
That is not the standard system-wide, however. Extra trains for the AML typically are in the 356-359 range for the Wolverine, 360-363 for the Blue Water, and 372/373 for the Pere Marquette.
I was trying to find out 1297's route. Just for fun I tried looking at the Empire Service schedules (between stations on a particular day - not the "printed" ones) and it didn't show up.
We've mentioned this train before. It is a scheduled deadhead train that operates off Sunday only 288's equipment at NYP. it departs in the wee hours of Monday morning.