Release 2021b moved to 'backzone' nine zones whose timestamps since 1970 were duplicates of other zones, as part of a process that started in 2013 in the interests of removing prior inequities, one step at a time. If we were to continue this process in the same way, we could install the attached proposed patch which would move more zones, chosen via the same procedure used for 2021b. It strikes me, though, now that Stephen Colebourne has established a mechanism that can let downstream users keep the duplicate-since-1970 zones, that it may be a more effective use of our time to move the rest of the duplicate-si ce-1970 zones now, while no urgent changes are pending. This would move another twelve zones if I've counted correctly, and would let us more efficiently turn our attention to other issues. Comments welcome.