I don't know why you would think that Ca gets locked out at 6.5 and below. 6.5 is as close to too high as I'd want to get.
Nobody here really knows what a Ca def looks like. If you see pics of Old fan leaves with a def it can't be Ca, because Ca is immobile and cannot be translocated. It tries and may redirect from edges of older leaves to new growth.
But the Ca def has to show on new growth first just like the other immobile elements like Fe.
I'm no organic guy, but I'm with the 'you overnuted' crowd.