Now, were their experiences real? Did we make them real by marking them with a 1 - by applying the logical filter using a causal computer?

You can apply the brute-force/postselection method to CGoL without timetravel too... But in that case verifying that a proposed history obeys the laws of CGoL involves all the same arithmetic ops as simulating forwards from the initial state. (The ops can, but don't have to, be in the same order.) Likewise if there are any linear-time subregions of CGoL+timetravel. So I might guess that the execution of such a filter could generate observers in some of the rejected worlds too.

There are laws of which verification is easier than simulation, but CGoL isn't one of them.