This is what is called an assignment of tenancy. See RTB website. I don't see any issue with you backdating an assignment of tenancy once there is no intention to deceive anyone.I had a lease a few years ago with a couple who took in another tenant. The couple left and the extra tenant took over the lease
It depends on what the circumstances are but a tenancy is not a very good proof of anything. A utility bill would be better.looking for proof of residency.
It's not clear from the OP that this is being sought. If there was a de facto assignment of lease on a certain date then it is fine to put in place paperwork that attests to this fact.You would be providing fake documentary evidence to something which is not true.
This is what I read as looking for the lease to be back-dated; i.e. to state that Tenant B was in residence at a time when they were not.wants her name put on the old dated lease