Zone stamps are associated with Zone Categories, which in turn are attributes that are embedded inside a project. Simply loading a project in a newer version, and even loading a newer library, will not change these.
If you want the old zone stamps, you'll have to load them. If you want to use the new stamps, you'll have to change your zone categories to specify them.
Cheers,
Karl
One of the forum moderators
AC 28 USA and earlier • macOS Sequoia 15.2, MacBook Pro M2 Max 12CPU/30GPU cores, 32GB