The excommunications of 1054 have long been seen as a pivotal moment in the Great Schism. But recently I found that some people apparently doubt that the excommunication of the Patriarch of Constantinople was actually valid, because the pope that had sent the representatives, Leo IX, had already died when the excommunication was announced. The linked Wikipedia article calls its validity "doubtful," while a different article, this time without a source, simply says that because Leo IX had died, "the excommunication was thereby invalid."
Yet I also know that in 1965, Pope Paul VI lifted the 1054 excommunication – which seems to suggest that it was valid. And Everett Ferguson (Church History, I, 19.V.B) gives no indication of their invalidity.
According to Roman Catholicism, then, was the excommunication of the Patriarch valid? Were the representatives able to validly excommunicate only until Leo IX's death, or only until his successor took office, or anytime?