I think we've reached the limit of productive argument; the SIA, and the negation of the SIA, are both logically coherent (they are essentially just different priors on your subjective experience of being alive). So I won't be able to convince you, if I haven't so far. And I haven't been convinced.

But do consider the oddity of your position - you claim that if you were told you would survive, told the rules of the set-up, and then the executioner said to you "you know those people who were killed - who never shared the current subjective experience that you have now, and who are dead - well, before they died, I told them/didn't tell them..." then your probability estimate of your current state would change depending on what he told these dead people.

But you similarly claim that if the executioner said the same thing about the extra observers, then your probability estimate would not change, whatever he said to them.