Currently, the generated scripts Drop*.sql only uninstall functions and triggers generated by the same version of the indexer. That makes schema change migration difficult because if that step has not been completed with the previous version, it is not possible to uninstall the previous functions and triggers with the new version, and downgrading is not documented either.

So Drop*.sql should be regenerated with each new version of the indexer, and it should keep previously generated DROP instructions too.