You piqued my curiosity, so I looked it up in Denzinger 468. It reads "Si ergo Graeci sive alii se dicant Petro eiusque successoribus non esse commissos: fateantur necesse se de ovibus Christi non esse, . . ."
To me it is utterly clear that what Boniface is saying here is that anyone who says that they were not committed by Christ to the care of Peter, thereby denies being the sheep of Christ and cannot be saved.
But that is exactly what the Orthodox who make a primacy of honor/jurisdiction do not deny. They do not deny being committed in any sense whatsoever to the pastoral care of Peter. They deny being committed to that pastoral care in the way that others believe they should acknowledge being committed.
The dispute between Orthodox and Latin Catholics is not over whether all Christians are committed to the care of Peter. You do not deny (unlike some extreme Protestants) that in Mt. 16 and in John 21 Christ committed his Church/sheep to the care of Peter, do you? At one time it was common among most Protestants to deny this absolutely but a wholesale denial of it has never been characteristic of the Orthodox-Catholic schism. We are in schism, not in communion fellowship not because you deny any and all Petrine authority but because we disagree over the exact nature of that authority.
Boniface did not intend this as a blanket rejection of all Greeks. He wrote "si (if)" the Greeks or others deny all committedness to Peter they thereby deny being sheep of Christ. If he meant that the fundamental position of the Orthodox involves a denial of being committed to Peter, he should have written, "Since" ("Quia" or "Quoniam" or something like that) the Greeks and (not or) others deny that they are committed to Peter.
Even strictly grammatically the passage implies a distinction between those Greeks who make a blanket deny of any special authority for Peter given him by Christ (as some Protestants still do to this day) and those Greeks who acknowledge some sense of being confided to the pastoral ministry of Peter. I would assume you are included in the latter.
So the more "benign" interpretation of Unam Sanctam upon which Fr. Feeney was condemned in the late 1940s, a few years before the time you were in grade school (do I have it approximately right), is not a later whitewashing of an objectionable passage in Unam Sanctam but a fairly decent prima facie interpretation of the plain words. Your first grade nun (sorry for missing the fact that it was a nun, rather than "he" as I wrote in my earlier post) was teaching a crypto-Feeneyism. The Irish pastor was not just smoothing over your father's ire while secretly approving of the nun's Feeneyism. If the priest was familiar with the recent condemnations of the Feeneyites, then he was in fact giving your father the straight dope on the matter and was in fact condemning the nun's false, Feeneyite interpretation, though in a nice way!
I hope that this might make some sense to you now, after all these years of anger at what truly was an insult to you by the nun who was not accurately representing her own church's teaching but, like the priest said, may not have realized she was teaching condemned Feeneyism. (Or maybe she did realize it?)
You know, I had forgotten completely about Feeneyism. Its likely that the nun in question was a follower of Fr. Feeney and it is equally likely that the much beloved old Irish monsignor was not at all. 50 years after the fact I think I understand what happened. Thank-you! Funny how something like that can stick with one.