The tool could probably use a review with a set of “fresh eyes”. That is always worthwhile. (Look at the review OlliL recently did to improve and optimize the Verify Data tool.)
So this tool also leverages the preferences for average Generation age-based calculation and allows overriding within the dialog. So you could even do stepped refinements manually.
That is, you could run the tool with values that were appropriate before effective contraception became easily available and changed everything. Then use a custom filter to find placeholder events after that date and DELETE those Events. Then run the Tool again to generate placeholder Events with post-contraception values.