When, against my better judgement, I got persuaded into writing the beta 40th piece for the LMC rag I studied all this stuff in some detail, Beta history is not well documented even by lancia so confusion abounds. The parts books are one of the best sources to confirm changes but it takes forever to trace stuff that way, sales brochures, of which I have quite a few (hundred or so....), are good reference material but often inaccurate particularly around the s1 s2 changeover when they often used s1 photos in s2 brochures!