TCS Background verify only relevant experience or all experience

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I have recently selected for TCS. I have total 10 years of experience. In Company A(Training Institute) 2 years, Company B(Training Institute) 3 years and Company C(Software company) 5 years. TCS consider relevant experience only 5 years for Company C only.
My question is TCS do background verification for all previous 3 companies or only last company as it consider relevant experience for that only.

Note:- My First company A(joined in 2011) is closed now and I only have joining & experience letter of that company. Salary received in cash so no bank statement or nor Form 16.

Kindly suggest it create any problem in background verification. I have already inform this situation to my recruiter HR.
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