Retrospective agreement is valid and can be made on  stamp paper of back dated. 

You can have backdated agreement of July 2019 as stamp paper is of July 2019 

- Yes , A restrospective agreement can be made legally. 

- You should add a clause in the agreement that the agreement deemed to have commenced from the retrospective effect, as both parties of the agreement agreed , and no party of the agreement having objection for the same . 

1. Rent /Lease agreement has to be mandatorily Stamp Duty paid and Registered, BEFORE start of Rent /Lease period.

2. By virtue of the above, IF Rent /Lease agreement is execute for retrospective periods, THEN it would amount to suppression /concealment and would invite prosecution leading to confiscate of document & penalty.

Stamp paper of later date cannot be used for a transaction of leave and license of a tenure previous to the stamp paper date

Your query can be answered by a local advocate based on the proper information you may furnish to him/her including drafting the rental agreement as per your requirement following the legal procedures as envisaged in law.

agreement executed with restropective  effect are valid in the eyes of law. 

Yes you can do it if both the parties are agreed for the same. 

See you can make agreement from past date mentioning that you and tenant orally agreed these condition and now you are reducing same in writing the agreement validity period can be mentioned.

NO. Agreement will execute of present date. In it, can be mention that tenancy is effective from that date and will be for this much period or up to that date.

No you cannot execute a back dated agreement on stamp of 2019.