I must be really missing something. Would really appreciate if you could please point out a line in my post above where I go wrong?

SPY options expire at the market close at the day of expiry, so for an option expiring on Wed, SPY close price on Wed is the one used for settlement.

This price - the unadjusted SPY daily close price - is taken by Zorro from a "*.t8" file.

Is this correct?

Workshop8 - my first example - specifically has "History="*.t8" - so Zorro is only aware of unadjusted SPY prices..