I appreciate that there are 'exception to rule' examples of just about anything gort.
A horse won a race after 4yrs of outs yesterday and that's one horse I wouldn't have liked to have been following since it's last win. The general rule to sack horses that haven't won for at least a year [99% never win again] isn't going out my window because there are exceptions.

As for spells, horses can run an 'easy' distance race and a 'gut-buster' sprint [Takeover Targets last run looked like a gut-buster] or vis-a-vis. 2 to 3 weeks between races is an accepted standard of rest regardless of the type of distance a horse races.