I knew that was coming at some point!
I needed to seed a new copy to remote site because I was migrating VMs from one vcenter to a new one so that resulted in a full backup anyway.
I probably could have tacked that onto the original, but then I'd have (presumably) had to "seed" the whole 42 restore points as well.
In retrospect i guess what I could have probably done is map the job back to the original files, then created a local backup copy, and seeded /that/ to the remote site, but I was kind of having a clean-up anyway (revised job name, different repository placement etc.) so just started afresh.