"The model's name was derived from 'PL' for 'Panhard et Levassor' (the original full name of the company), with the '17' coming from the sum of 5+6+6, being 5 CV (fiscal horses, in the French power rating system) plus 6 for the car's six seats, plus 6 for the car's economy of 6 L/100 km ...."
As noted in my Dyna Z post, styling was aerodynamically influenced. But the facelift attempted to slightly disguise that.
Unless noted, Images below are of cars listed for sale.
Dyna Z front quarter view via Mecum auctions. The main PL 17 sheetmetal change seen from this angle was for the grille / front air intake. Otherwise, modifications were trim additions.
PL 17: The bumper is simplified. Turn signal lights are moved from near the doors to the ends of the car. Chrome splashes are over the headlight assemblies, then trail along the front fender. That's probably a fake airscoop extending across the front of the hood: not all PL 17s had this. The windshield surround is now chrome instead of black rubber.
Dyna Z rear end view.
The greatest shape change was at the rear where the trunk was raised and its opening cutlines changed. Some cutlines correspond to chrome "eyebrows" over the taillights.
Showing B-pillar hinged doors.
The changes, especially those at the rear, have the effect of reducing the visual and actual curved shape of the Dyna Z. All this was to bring the design more into line with comtemporary styling fashion.