Edward, I do not doubt all this information, but the most important thing is to go backwards, not forwards. that is the best genealogical practice.I know I am descended from Don Rodgrigo de Alderete. At the moment it is most important to find his ancestors. Everything else is just speculation. It is entirely possible that there may be several families with the same name, with origins in several locations,all called Alderete (I have read that there are a number of locations called Alderete in Spain and Portugal) and that some Alderete are not related to others. Who is your oldest Alderete ancestor at the moment? Does he tie into Don Pedro's Tordesillas line? If he doesn't, then there are two possibilities 1)that he ties in before Don Rodrigo 2)that we have more than one Alderete family with different origins. We can only establish this by working backwards. Cheers.