Looking at your way of doing it is quite brilliant Noel (I may ditch mine)
The drawback is that just because Classic has a pair, doesn't mean that there weren't more than 2 full siblings, or others that had a pair but the sibling did not qualify to be included in Classics db
So still looking at a lot of HRA searches
Due to cost of O/S searches would probably have to restrict it to NZ and Aus horses