Originally Posted by
flyerCO
Call back. HUACA is really all can do, or try Twitter. Does it show Z when searching for the whole route or only as a stand alone. There may be Z on AAA-BBB but not on AAA-BBB when flying AAA-BBB-CCC
And for a 3-segment-per-direction route it's possible that your particular AAA-BBB-CCC-DDD doesn't even show up on Expertflyer, in which case you have to depend on what Delta tells you, and annoyingly many agents get it wrong. That said if they told you that Z was available for purchase, not for upgrade, it sounds like Z probably is available, and they're just wrong that there's a distinction between purchaseable Z and upgradeable Z.
In my experience calling during weekday business hours is usually best, I've gotten some really bad advice from weekend agents. Though with the holiday this week the most senior and thus (usually) most competent agents may be out all week.