I got the "incorrect DEF fluid detected" message earlier last week, and made an appointment to bring it in yesterday. Two weekends ago I added 2 gallons of DEF purchased at my dealership, which showed "packaged 6-15-15" and "best used by 6-15-17". Also over a few weeks or so the "check engine" light would come on and later go off intermittently.
Got a call this morning and they had this issue corrected (at least, I hope). They found code PO2EE and replaced the CAT (p/n 68243268-AB) under RTT 15-093, and performed RTT14-075 inspect DEF and reroute DEF line. They said that the "check engine" light showed the PO2EE code which was included in RTT 15-093.
They also performed RTT 14-087 flash HVAC module, RTT 14-107 flash PCM module, RTT 15-098 inspect EGT EGR temp sensor (cleaned and reinstalled), RRT 14-050 flash BCM module, recall P641 flash steering column control module and TSB 21-012-15 flash TCM for the shift enhancement (bump on 2-1 downshift and improved upshifts).
Although I only drove it home 10 miles, the shifts are a lot better and it doesn't hesitate quite as much on acceleration from a stop.
It was a very good dealership experience - they knew what to inspect and did it, had the parts in stock and got it done in one day, and got me a rental car under the extended warranty without a hassle.
The Asst. Service Mgr who wrote me up said they've done quite a few of these, especially on earlier production GCs (mine is a Dec. 2013 build).