Probably you are right: the pictures are not dated, but Pininfarina was used to putting a progressive number to the cars pictured.
This is no. 693, so it's later than the second version of coupe (the one wiht panoramic rear window) marked 673, that should be 1955. The most close later I've in my archive is the 600 Eden Roc, number 718, that for sure has been unveiled at Geneva 1956, in March.
So, this one should be late 1955 or early 1956.