a "good" horse may be spelled after a few starts because the connections think that they are on to a "winner".

They believe that they can re-assess its career and achieve greater prizemoney in the future.
If it has very good performances in minor races early in its racing life, the connections will tend to place the horse in greater PM races upon returning.
If one can pin point these horses, with a return in a race which it is regaining fitness in the same class which it won earlier on. Bingo.