OptionalcreatesOptionalreplacesWhether this manifest may replay over a database that has already finished a DIFFERENT generation. Absent, which is the shipped pack, means no.
A restore sets it, and that is the whole difference between the two directions. Replaying a newer pack over a site that has been running and writing for months would produce a database that is neither; replaying a BACKUP over that same site is the entire point of the backup.
Optionaltables
The part of
manifest.jsona replay reads;scripts/pack-sql.tswrites considerably more.