Carding Races

Yes, that is generally the case.

A lot of races, if not most of the allowance, maiden, and claiming races are actually added to the schedule by other players. I frequently buy races, usually shortly after my horse has just raced, especially if the range/location/level is rarely offered. If you buy them at least 4 weeks out you get a 10 credit discount.

Poly races are thin on the ground, so if one of my horses turns out to be a poly specialist, I usually don't wait for weeks hoping a race pops up. I'll just buy one right after it has last run. Allowance/claiming races are usually around 30 credits, so pretty cheap.