In case comps are wanted,
this car just sold a few minutes ago on BAT for $70,800. I believe BAT also has a buyers fee, and of course, the car probably will need to be shipped. That was for a well equipped '17 with a KT 460 tune and 7K miles. So a 71.5K trade offers sounds good to me. The used Evora market is looking up. These cars couldn't crack $65K three years ago on BAT with no miles on them when offered by a dealer. Wait until they are discontinued.
I think the difference in sales prices for '17s vs. 18s will of course favor the newest car with lowest miles, but the delta between the two model years is going to remain quiet slim. There isn't really much to choose between them apart for CF available packages on the 18s, so what one 400 sells for should probably be comparable to another even if it is a later model year. I think these two can be compared directly, taking into account that one was sold at auction and the other traded, one had CF, the other an expensive KT upgrade.