if you collect railways of the 20s 30s or even older, much is very rare.
For example.
Karl Bub postal car in yellow, never seen a second.
Bing, factory error, NYC and PRR on the same car.
Bing Fish car as NE, never made regular, hand painted prototype
Fandor Fish car, never seen a second
Karl Bub Observation, very hard to find
And new in the collection but need a bit repair and a new driver.
Brimtoy All Clear Loco, every few seconds the driver looks out of the window. Worldwide known at the moment 3 of them.
Arne