Yup, 63214A on block isn't exactly safe but I just did it anyways since it's flashy lol
But yeah, I'd recommend sticking with 22a instead.
I tested out the ground combo > 5A 22A > 623B, it connects but I can't combo into knife loop, the knife ends up pretty far away for you to be able to pick up. Unless it's done on a certain range I don't think it's possible, I might be wrong.
After 2C delayed 22A oki works (same oki as 63214A: left, right, high, low) I was able to do a crossup j.6B with it by accident too. It's probably specific though (due to hitbox of certain characters and whatnot)
With all this new info I'll probably update the wiki.... someday.