Yesterday, I booked two tickets for relatives RT PVG-MSP on different PNRs in Main Cabin and then went to upgrade the TPAC segments to C+.

The DL website quoted different prices for the C+ upgrade for each PNR (~2000 CNY for one and ~1300 CNY for the other). This difference appeared on multiple devices.

Both pax were FO and both outbounds had identical routing, base price, fare basis codes, and fare class (X). Tickets were booked within a few minutes of each other in separate private browsing windows. The only difference was the return date.

Is this evidence of tiered pricing in action, or am I missing something? Could the return segments be influencing the pricing?

FWIW I ultimately cancelled and rebooked the tickets directly into C+ for much less than what DL wanted to upgrade all segments (both online and over the phone, on the order of hundreds of dollars in savings).