It must be a Lancia thing - not much inventory control! I was going through a load of Aurelia heads the other day with my father some S4, some S5 and some S6. All had the same casting date and number (1954) but different machining to suit the different series.
I can just imagine the casting department going hell for leather over one side of the site to hit their bonus, with not a thought nor managment intervention for what was coming out of the gates at the other end
I wonder how many remained and were scrapped when production ended ?