Retrospective Effect of housing deed

As per the existing laws you cannot register the deed with retrospective effect, so without valid deed you cannot get any HRA benefit. 

1. The overall point in making an agreement is to give a legal consideration and make it binding between the parties to the agreement. If the backdated are valid if would totally nullify the effect of entering the agreement in the first place. 
2. Memorandum of understanding could be backdated but it cannot be backdated for the event which had already taken place. In your case paying of rent is the event. 
3. Hence, retrospective effects are only for laws and regulations and it cannot be stretched for legal agreements. 
4. Our expert view in this absolutely correct and in conclusion rental agreements cannot be entered with retrospective effect. 
Please correct me if the above interpretation has an alternative view.