developers have notarised but not registered POA,can they sell

I have intended to purchase a flat in a building from namely Mr. Z . He have previously purchased the said flat in 2012 from the developers M/s AB . The land on which the building have been constructed did belong to Mr. A , Mr K and Mrs L. They A K L altogether made a notarised but not registered agreement between them and developers M/s AB to construct a building and filed for mutation and sanction, which they got in 2003, in they name of A K L. Now later Mr K and Mrs. L gives notarised but not registered POA to Mr A to sell and take advance of this property in 2006. Then in march 2012 Mr Z purchased the said flat fro M/s AB and Mr A through registered deed. My question is will that registration from M/s AB and Mr A to Mr Z will be get nullified or void as there was no registered POA by Mr K and Mrs L to Mr A at the time of selling i.e March 2012 as it is after 2011 supreme court ruling about general POA. And if i purchse the said flat from Mr. Z the title deed will be subsequently nullified. please advice, thanking you in advance.