Confirmation of Experience from prior employer

"You will need to be able to get written confirmtion of that experience from you prior employers. We absolutely do not want you requesting written confirmation now, but need you to understand that if you didn't have the experience or cannot get written confirmation of that experience, the labor certification application will fail."

My lawyer is preparing job posting for my LC as EB2 category. I was asked to get written confirmation of experience from my prior employer later. I am confused with the following terms:

1. Is it a must to provide the written confirmation from my prior employee as a step to file LC?
2. I have got reference letter with company letter head from HR of my prior company, but did not mention my detailed responsibilities and skills, is that what the lawyer wants or seperate letter from my prior manager?
3. If I must get the written confirmation letter from my prior manager, must she write it in company letterhead?


Please please help me in this, really frustrated.