As evieceli "sez", there are many opinions so I'll add mine.
I have a 73 Spider Veloce and it's VIN starts with 115. It doesn't bother me when ordered parts as to which is listed, 105 or 115, they have always fit . Whether they came from the UK at Classic Alfa or Colorado from Centerline, they work for me.
When doing sparse reading on the Spider, I noted the designation of the S1, S2, S2a, S3 and the S4. Yes, two classifications of the S2.
From records we had no imports released during 1970 (those of you old enough to remember the Russian steel issue?). 69 of course was the S1, 71-74 were the S2, 75 thru 82 were (Kammtails) the S2a,, with the wonderful regs on "safety",, thank you Mr. Nader.
So hopefully, you get the idea, by the way, those 71's,, should have been 70's if they could have got out of the docks.