Hello Mike. I'm more and more convinced that you've got the correct Catharine Killey and I've been wrong for a long time. I hope some of the people I've misled will see this and make corrections. As you say, genealogy can be infuriating. Hanging onto mistakes is one of them, and even more infuriating is when it's one of your own. That's why I'm afraid to publish anything.
One thing I feel confident about is that the 1781 will of Philip Killey that Francis's summary says "bro-i-law john gelling supv" belongs to my Cath Killey. There's no other John Gelling connected to a Killey at that time. However, I didn't get anywhere trying to find anything else to connect Catharine, Philip and "bro Wm" together. Everything I tried seemed possible but nothing very strong. I only found two baptisms for a Philip Killey, one belonging to your group and the other 1727 Malew s/o Thomas, which didn't match to anything helpful.
I don't have anything for an Edmund Garrett, but it's not a family name I've done research on. Maybe somebody else on the Board has something?