Biappa approved plot mother deed

I was scrutinising documents for buying a residential plot which is BIAPPA approved. The plot has been purchased by the seller five years ago from a developer who has all the mother deeds of the complete layout in his name who is still the custodian of the documents. There is a Katha extract in the name of seller and the taxes have been paid uptodate. The encumberance certificate shows the name of seller. The present seller who owns the small piece of plot in the layout has executed a sale deed with the developer. The executed sale deed with the developer do not have any clause on rights of selling on the piece of plot and also do not have any NOC from the developer. Also, there is no clause in the sellers sale deed on wheather the mother documents of the layout will be handed over to the Owners society or Owners welfare association. Who has to be the custodian once all the plots in the layout are sold by the developer? Is it safe to buy this plot?