I didn't read too far upthread, so please don't skewer me if this was already discussed...
A few weeks ago, I waitlisted SFO - BOS for later this month using an RUC. Saw the double seat map for a few weeks with D1 entirely blocked out on both seat maps. Checked this morning and the first seat map said that my seat could not be assigned (though I still had my original C+ seat) and the second seat map showed 9 available seats in D1 (it was previously all blocked out), though I couldn't select any seats. Sent @
Delta a DM on Twitter and the very helpful agent confirmed the upgrade and put me in 1C.
Long and short: if the second seat map shows available (not blacked out) seats, it's worth checking with an agent to see if the upgrade cleared but just wasn't processed yet.