That is correct, thank you for pointing out. I think Canterbury must be an oversight in relation to an old setup, which since has been rendered obsolete.
Good ideas, we will note them as future additions.
No problem, and thank you for considering my ideas

Other religion suggestions I've thought of in the last few days...
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Pelagians: In addition to the 'give alms' decision I proposed earlier, I think they should also have access to the 'reject vices' ambition that Buddhists have. A major Pelagian argument was that humans, being inherently good (as they were created in God's image), untainted by Adam's Original Sin and having full free will, could basically choose to stop sinning if they tried hard enough; Pelagius himself advanced this argument to counter the dissolute Roman aristocrats and orthodox clerics who defended their sinful lives with the 'I can't help it, I was born inherently depraved and sinful' line.
Perhaps Pelagians should also have the ability to launch a crusade, called a 'March of Good Example' like in Lux Invicta, if they get strong enough to create their religious head? Since in Pelagian theology, sinners aren't victims who can't help themselves and who need the grace of God for salvation, but criminals who need to stop being criminals of their own volition, it could logically follow that they may come to believe in launching holy wars to both 'make an example' of those whom they consider recalcitrant sinners who won't stop wallowing in sin and heresy, and to set a good example themselves by risking their own lives to liberate holy sites & peoples from rival sects or infidels.
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Aquileians: Access to the Catholic holy orders if they survive long enough & the Nicenes don't schism, maybe? They seem to be a very Western-oriented schismatic branch, and to my understanding they were literally 'more Catholic than the Pope' in the sense that they refused to join the Second Council of Constantinople (and eventually, the Pope himself) in condemning three certain authors' works as part of an attempt to appease & bring non-Chalcedonian Eastern Christians back into the fold.
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Hephthalite religion: It's described as a syncretic faith combining native White Hun/Tabitian, Zoroastrian and Hindu influences in-game. Perhaps it can be given the ability to be reformed, giving it a religious head and the Indian religions' 'hard to convert/hard to be converted/no religiously-induced revolt risk' mechanic?