Deemed Conveyance for housing society in Mumbai

We have a co-op Housing Society registered in Mumbai and having 50 members and 50 apartments allotted to them. The building is in Mumbai and 46 years old. The builder and Society signed and filed the document for registration to sub- registrar in year 1972. However, the builder did not submit Income tax certificate to authority and the document remained pending. Several attempts by the Society intermittently made with different office bearers and with different fora e.g. Builder, Federation, State Govt. did not bring any result. Mean while the where about of builder ( several parties) are not certain now after several decades. Further, the Society records show that the copy of the document signed with the builder is not available in its records.. The question is 1. How can this document be obtained/retrieved? 2. What is the status of this document which was signed by builder and filed for registration but not completed due to non-submission of I.T.clearance by them? 3. If the builder has erred in presenting I.T. clearance certificate, can the society be granted conveyance now? 4. Should Society pursue the recover/ retrieval of old document or go for deemed conveyance.