MY15 the original
MY16 added separate parking brake calipers on the rear.
MY17 mild interior facelift, replacing the infotainment screen
MY18 redesigned front and rear bumpers, body colored side skirts and added optional LED headlights
The MY18 has three exterior lines, Ghibli or base, GranLusso, and GranSport, much like Mercedes had Elegance and Avantgarde lines in the past, which are nothing really but appearance option packages. The GranLusso and the base (like the one in your spot) share the same exterior bumpers design.
I think the quickest way to tell which is which is from the front. The original's lower grill looks like a frowning mouth, the 2018 base and GranLusso looks like a smiling mouth, and the GranSport looks... well... more sporty, like blades :)
Also, in the case of SQ4 cars, they've changed sometime in 2017 the Q4 badge (with the red 4) to all chrome an SQ4 badge.