Here's a similar offer I got today, but it does in fact mention special inventory. Anyone else seen this language or know what bucket the inventory comes from?

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Dear happysolti,

We noticed you were searching for Saver Award flights on
united.com recently. We are sorry if you couldn't
finalize your travel plans to XYZ. For certain flights,
Saver Awards are in high demand, and we know this can be
frustrating. If you couldn't find Saver Awards for the
dates and destination you wanted, we want to help.

To thank you for your loyalty to Mileage Plus, we are
offering you a special service. Here is how it works:

<> Call United Reservations center at 1-888-XXX-XXXX
anytime between now and February 01, 2010.
<> Our reservations agents will search a special inventory
of Saver Award seats and make every effort to meet your
needs.*

We're committed to making it easier for you to use miles
and working hard to make Mileage Plus your preferred
loyalty program. Call us now at 1-888-XXX-XXXX, and let us
help.

Your Mileage Plus team
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Also in the email is the offer code: MPS320. Among the T&Cs relevant to this discussion is, "United Reservations handling fees are waived for the participants." Also, "Offer is by invitation only, restricted to the original recipient of an email invitation, and available on a first-come, first-served basis." Other T&Cs look like usual for award tickets.