Do USCIS verify skill letter experience tech worked and company details?

I have a Query, I worked for company A-3 yrs and company B 6 yrs, now company A doesn’t exists and my colleagues are not in touch, but my attorney is asking all my pas company letter in Letter head.

Do we need Company A 3 yrs letter also for processing GC, i think 5 yrs exp is enough for this, is it?

Do they(GC team) verify my Company A details, if i give my company A Experience and relieving letter and former employee affidavit(if i get).

In this case how i can proceed?

I think you will have to find someone who can vouch for you and your work in Company A on a plain piece of paper.
And that someone should be the one who actually worked for you. get in touch with them.

You only need last 5 years for your skill letter. If your company A was the first one that you worked for, then you need not worry at all.
Just take the skill letter from Company B and that should be good enough.

They can verify any document that you submit.
If you are NOT sure about legitimacy of any document, i would STRONGLY advice to NOT submit it.