Hi
It is probable that the property was constructed in the year 1980 and probably they had an municipal approved plan.
It is also probable that any irregularities in construction might have been regularised, given that the building is 39 years old.
However you can still check with Town planning office of brihanmumbai municipal corporation to find out whether there are any pending cases against society pertaining to violations in building construction.
Also you may check property tax assessment receipts to see whether the society is paying any penalties for deviation/violation etc.
Hope this information is useful