I believe it is as follows (based on what has been stated or
implied, so most of this is unconfirmed):
: established member in "Taking Wing", admitted 2360
: Probable member based on "Orion's Hounds" and "Losing the Peace"
: Unknown- if they are a member, which is possible, "Over a Torrent Sea" established they're a reclusive one who maintain an enigmatic distance from other races.
My impression was a protectorate or ally of the Federation, not a member.
: I don't recall much evidence for any particular interpretation.