A suit seeking declaration of title by operating the law of adverse possession can be filed after 12 years of continuous possession of the property
If a person claiming title or ownership on the basis of the registered title deed on his name, fails to file suit for recovery of possession, within a period of limitation, his right to recover the possession of that property also extinguishes. If such situation occurs, a true owner extinguishes his ownership over the property.
You have stated to have occupied the property on the basis of unregistered sale deed around 4 decades ago, hence it would be better that you get the title declared through a court of law
In your case even if you have rented the property , you are termed to be still occupied and cannot be said that you are out of your possession.
You are in continuous possession of the proeprty hence if there is any dispute regarding your title at the time of redevelopment then it is pertinent that you need to establish yor title to the property in the legally valid manner.
If you are not knowing the name and address of the original vendor you can send the notice to the vendor to his last known address after which you can file a suit.
This is a bit big subject hence you need to consult and discuss in person with an experienced lawyer, and if you are really serious to solve the issue then you can take steps to solve them legally.