Why tcs ask for experience letter from all previous companies

If i I'm for job in tcs and previously i worked in 4 companies, is it mandatory to submit the experience letter from all 4 previous companies.

One of my friends who previously work in a startup for 2 months then he joined wipro,

And he didn't mentioned the 2 months experience anywhere, simce this 2 months reflecting on epfo portal tcs is asking for 2 months experience letter. The previous organization is got giving the experience letter even if he is ready to pay penalty, he submitted all proofs like offer letter, resignation acceptance mail and form 16 still tcs is asking for offer letter only.