What information would you want imparted? I've tried saying "this is a set of reels in D"

This is precisely what I meant when I said Given a key, the basic chords are bleedin' obvious (aren't they?).

What more does a bunch of guitarists need? Yet, speaking as a fiddler, I've sometimes asked what key they're playing in (it being just a little unclear from the shapes I'm looking at) and they don't know. Or else starting up a tune at a session (that doesn't happen very often!) to be told: That's not in D (or whatever) and that's what we're playing in today.

What was I saying about playing by numbers?