I think you have stumbled across one of those urban myths concerning horses that have run well at the distance.

I found , using the GTX program, that horses that performed well at the distance did not perform any better than horses that have never run the distance.

As a matter of fact , the horses that have never run at the distance performed better than those who had won at the distance - weird.

That's over 40,000 races.

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Cheers.