C. Clark has a point that testing and developing the new car can compromise their performance/development with current one. As he writes in 2016 VW tested 2017 on most pre-event tests, often dropping the 2016 car completely. Imo it showed as by mid-season 2016 Polo wasn't the clearly unbeatable car any more.

Lluis at WRCWINGs for some reasons misses the omission of the small front side-planes ahead of the doors and more importantly the completely different car sides/floor extensions.