It really depends on what type of data you are going to validate. Normally, public company’s information has some degree of transparency to the general public and open more data through the paid sources. To validate private company’s data will be challenging. But still, there are ways to get around such as investigate from their counterparts including suppliers, customers, business partners, and consultants. Design specific forms or questionnaires for the “outskirt” type DD. Then matching what the finding with Data room.