Why do we have to use several sources of information to evaluate a company?

Thanks for the invitation.

It is just because to know more accuracy of financial information with the actual effect of a Company. For this external source of evidence is more reliable. 

Thanks for invitation, 

To be  sure and have a clear picture of its actual financial position in very a transparent manner.  

To ensure the validity and accuracy of the information used in the analysis and evaluation of the company.