Not necessarily, right? If they have room in the higher cabin to op-up into, they have room to do a birthday upgrade.

In answer to cy1978hk's question, Who knows? Op-ups are not a published benefit or a right for any status level. It's totally at CX's discretion, for operational reasons. If they're oversold in a cabin, they could decide it makes good commercial sense to offer a birthday upgrade to a SL instead of a "regular" op-up for a DM. The DM isn't in a position to complain, since he got the cabin he paid for and should have expected to fly in anyway.