I attempted to give a better reply/help/documentation at https://help.openstreetmap.org/questions/21804/buildings-just-demolished-just-delete-them?page=1&focusedAnswerId=60550#60550 and https://wiki.openstreetmap.org/wiki/Tag:demolished%3Dyes

Thank you for giving me info where you looked for help, hopefully next person will have a better documentation!