I was watching Sky and from the Mounting Yard they were dismissing runners due to state of their coat; that they weren't quiet "ready". It occurred to me that the horses don't enter themselves in a race, circle a day on their calendar and make sure that they're in shape in time. The first up stat in the formguide seems to imply that they do.

I do suppose the stat is as revealing as others, like their career place rate; for example. That is: not very - without taking into account the likelihood of success in each of those races.

While there's scope for individual horses to be managed differently, I imagine that trainers would shy from re-inventing the wheel (and likely the more successful, the more reluctant). The linked thread seems to point pretty clearly that trainer-specific, rather than horse-specific, first up stats are a better indicator.