No, Walter. This is the wrong way of looking at the question. The saints we have recognized that the EO don't recognize or vice-versa are the saints of that respective communion, and hence are appropriate to ask for the intercession of within that communion. It says nothing of the effectiveness of the prayers, but rather the appropriateness of the saint within the given communion, e.g., EO will not ask the intercessions of St. Severus of Antioch, just like OO will not venerate or ask the intercession of Pope Leo of Rome. But that is not the same as saying "the intercession is meaningless" or something like that, because we don't pass judgment in that way on what goes on outside of our communion. It would be like saying God cannot work outside of our Church, when we all know that God can and does work outside of the boundaries of our communion, or else many of us wouldn't be in the Church in the first place (notice how many converts there are here from Protestantism, Catholicism, etc). So at best we can say "no, we do not recognize this person as a saint in our Church", or "yes, we do recognize this person as a saint", but not "prayers are meaningless". Any supplication that God answers is by definition not meaningless, but that does not mean that we'll accept just anything as appropriate in our respective communions. Does this distinction make sense?