Good point about only a 1/12 warranty on the 2018 CPO.
Makes a 2017 CPO look good with the 2/24 warranty.
Just seems like 2016 has a lot more depreciation...i guess it's whether that is worth the shorter warranty period. How much you want to roll the dice.
Other than age, the 2016s and 2017s are fairly identical. The 2017 is pretty much a carryover of the 2016 with nothing significant changed. With the facelift in 2018 came a bunch of minor changes, LED DRLs and tails standard but also less content elsewhere. The base S 2018s have a seriously de-contented infotainment system. CD, HD radio, Sat and compass are gone. You need a higher trim to get these for 2018 while they were standard on all trims in 2016-2017. 2018 also started stripping little-known parts away like the hood insulation, full battery cover, insulation under the steering column, slide-out drawer under the driver's seat, illuminated overhead console buttons, A/C vented glove compartment, etc... things VW figured no one would ever know about or care.
So yeah, if you can get a 2016 with a lot more depreciation already, that could be a better deal than a 2017. But again, one key to maximizing the warranty is to check the Carfax to see when the car was first registered. Finding a 2016 that was bought mid 2017 might give you an extra 18 months over one that was bought in the beginning of 2016.