Skills on experience letter for I-140

[A4PP]

I am about to file my I-140 And I am in the process of getting experience letters From my current employer. My immigration lawyers require me to add the skills C++, HTML, and Django to the experience letter to increase the chance of approval. I have not used these skills at my job at this employer, but lawyers are requesting to include these skills on the letter for successful approval.

 

 My manager is willing to add these skills  to my experience letter and sign it. I have the below questions-

1. Once this Experience letter is provided to USCIS as part of I-140 petition, does USCIS call or email this manager to confirm these three skills? 
2. In case if they do, what kind of proof does my manager need to provide back?

thank you for help