Hello,
I added a revision of "Reuse of the built modules (BMI)" paper addressing the Cologne comments:
https://isocpp.org/files/papers/P1788R3.pdf

The main changes/additions are in the "When BMI cannot be reused" section discussing

  * what info ("module recipe") is needed to be able to re-build a module (module source only, possibly by using a different compiler) in "locally built BMI" and "installed BMI" cases
  * who can produce this info
  * where it can be stored

Thanks,
Olga