The question was about the value of keeping old catalog backups and therefore I think I am asking about something different, which is not covered by your response. My question(originally to #
john.margetts ) is to do with the relevance of the old Catalogue backups to the Pictures folder. If you have a number of old Catalog backups ( e.g. several up to a year old), how do you relate the oldest Catalog file to the Pictures folder, when the Pictures folder will have had considerable additions to it, which are not in the older Catalog files. I keep a number of Catalog backups, but no more than 6 over the past say 6 weeks. Therefore I don't see the relevance of old Catalog backups if your Pictures folder has grown considerably in the meantime. I use Chronsync to backup my various folders, including the Pictures folder, where I have the option of archiving and synchronising deletions/additions. I just use the synchronizing option, as I'm not interested in keeping deleted images forever. Therefore my Pictures folder backups, (spread over a number of external drives) are more or less up-to-date with my main working Pictures folder.
Where the backups are kept is not important as LR will always know where all folders are, provided they are or have been imported to LR or set-up using LR.
In summary, there's not much point to Catalog backups once they have fallen behind the content of the Pictures folder, other than allowing for a few weeks lag.