Sell deed validity how many years without registration

1. Our grandfather buy a land( 1983) 36 years ago and took GPA and promissory note then made sale deed and not registered at that time in sub register office but got notarized from lawyer, and then he made GPA to my Father which is also registered ( 1992) Not showing in EC if its ok. 2, And then my father GPA holder made the sale deed to my mother which is registered in the sub registered office and we have till date EC in that it showing only my father made to my mother sale deed is showing but previous documents are not there in EC . Our grandfather and father died. 3. I have approached the sub register office and took EC From 1966 to till date in that only the recent sale deed is present is it ok. Paying Tax On time. Can i sale this property by keeping the above documents. How many year previous documents need to sale the property.