If there are two theories: there is finite number of actual observers in the universe and there is infinite number of them which includes all possible observers—then SIA strongly prefer infinite version.
However, we can use “I exist” for update only once. Now if someone asks second question—which of two theories is more likely, there is one civilization per galaxy on average and there are 100 civilizations per galaxy, there is no update from SIA. So SIA is a used ticket. However, we can still used SSA if we define exact reference class like: here is two galaxies and one is 10 times larger than another, there I am more likely to be?
If there are two theories: there is finite number of actual observers in the universe and there is infinite number of them which includes all possible observers—then SIA strongly prefer infinite version.
However, we can use “I exist” for update only once. Now if someone asks second question—which of two theories is more likely, there is one civilization per galaxy on average and there are 100 civilizations per galaxy, there is no update from SIA. So SIA is a used ticket. However, we can still used SSA if we define exact reference class like: here is two galaxies and one is 10 times larger than another, there I am more likely to be?