Thanks, Fujii for your response.
I ran the test you outlined. Killed postmaster. Start failed. But simply removing the backup_label file made the server to restart successfully.
There is no data corruption. Is there a scenario where data can be corrupted because of exclusive backup?
I saw your pg_extension where you put the old routines back with some additional checks... But I am hesitant to use the old functionality if there is really some issue that I am not realizing.
Thanks again!