I haven't read the book, just reacting to some of what you all are saying about what it says and most specifically the point about the Cats being abjured.
The Wolves-in-Exile were also abjured, but were welcomed back into the fold during the ilClan Trial. And look what happened with the Smoke Jaguars. Also the remaining Falcons could have easily been absorbed into the Wolves as isorla but weren't.
If there were a sourcebook that covered the Protectorate, I'm guessing what it would tell us is that Clanners all over are looking at these recent events and thinking this is a new era. This ilClan is willing to do things differently. To turn the page and start something anew. Abjured Clan, destroyed Clan. All past precedents and legal actions by the Grand Council or Council of Seven aren't necessarily the law of the Clans anymore. At least in the eyes of the government now ruling Terra, led by Alaric.
The Wolves alive today have a lot more reason to hate the Falcons than they do the Cats, and yet Alaric made a place for them and preserve them as a Clan. Sought to mend the wounds and look past the history.
I'm guessing the mood is one of "all things are possible now, we aren't necessarily restricted by historical judgements."
That's the only way it makes sense to me. It isn't necessarily what I would have assumed would happen within the Protectorate. But I can see how/why the Cats within the Protectorate might land on that viewpoint.
Keep in mind too, we're talking about the Cats. Insert appropriate "one of our people had a vision that could be interpreted to mean we should join the ilClan" and boom, it's done, in no time flat that becomes the majority viewpoint with people clamoring to do it.
No one else does historical pivots like the Cats. They have demonstrated a willingness to upend their entire society because they've decided that's their path now.