D Plan is for dealership employees who have been in "STARS" for 6 months and the dealership is Blue Oval Certified. It's the same as A/Z plan pricing. And Thunderbirds and F-450 up trucks are specifically excluded. I've been a A/Z planner for 36 years and can tell you this is the first vehicle I've ever bought at MSRP - but at this stage, Mom can have whatever she wants - at any price.
IF the dealership sold one to him at D plan price, they didn't get any assistance from Ford, and they will likely unfold the deal when they find out it isn't eligible. Most dealers wouldn't sell one to their best buddy at a loss!