Free patent OCT Real Estate Philippines

A OCT of a buyer has a note: This lot is covered by Free Patent Application No. (IV-2) 11278-B" ano po ibig sabihin neto? 'Coz they are selling partials of the land. They already have a DEED OF Extrajudicial Partition, and Approved Plan from Bureau of Land for the Entire land of 17,950 sqm. But I'm just purchasing 400 sqm.

Tama po ba ang papers nila para mabenta nila ang partial lands? And can i have my own title for my specific lot if i'll purchase it?

Pls enlighten me, ano mga possible probs in the future if meron man.

Thanks po.