Once a stallion reaches a certain age they have established a reputation for crossing well on certain lines of mares and from that point on there are few who are willing to step outside the line and try something new...both AP Indy and Rahy are old enough for this to be true. Although the Rahy-Seattle Slew nick gets an A rating from Werk the actual result of mating an AP Indy mare to Rahy and a Rahy Mare to AP Indy (though somewhat limited in sample size) has failed to produce much...so why keep trying when one has a much chance of success crossing on the lines that continually produce runners.
That said...Pedigree Ann can give you a much better analysis than I ever could...you should contact her.
