When customers upgrade, they typically test it out in a lower instance like dev or test, before upgrading their production instance. In this period any update sets being worked upon in the development instance might need to be moved to production prior to their upgrade.
Question: Is it okay to move this update sets from the lower instance on a higher release to the higher instance with lower release, in such cases?
In general it is not recommended to move update sets from a lower instance with a higher release to a higher instance with lower release.
If you have a dev instance with Madrid and prod is still in London, your update sets which are in progress in Madrid might have newer code changes which might not have the required dependencies in London.
Please refer to this community article discussing the same here.