Even it were possible to add a greater amount of "cases" to the retrospective analysis (e.g. by disaggregating the present US data to make the years independent and nonsequential, adding data from Australia or Canada, etc), I think it would introduce more uncertainties than it resolves. More fundamentally, it would remain retrospective analysis with all the inherent uncertainty about its applicability to the future.IOW, I'm suggesting that a 4% SWR could actually lead to a significantly lower success rate than 95% due to this data overlap effect; and, since we really don't know what the probability of success is, one should rely upon the FireCalc SWR that has never failed.
We say that "past results are not indicative of future returns", but in fact that's something each of us is forced to ignore, to a greater or lesser extent, as we plan for our future. Given that we are breaking the rules in this way, how much will be gained, in a practical sense, by improving the accuracy of the FIRECalc results? They provide a rough starting point.