Same client, L2EAD to H1 different employer, going for visa stamping

[MinalZodage]

Hi,

I am going for H1 visa stamping in dec 2012.

I came to USA in 2010 on L2. Then I got the EAD; started working on EAD got the Job1.

Then I changed my job for current client (Employer A - Vendor A - Client A) on L2-EAD on Feb 2012.

My husband changed his job; We both applied for H1 visa. I changed my employer but kept existing vendor and client as it is. I started working for same Client A from 1 Oct 2012 on H1B (Employer B - Vendor A - Client A)

I have some questions about the paper work.

• I am getting client letter from both my vendor and client. What start date I should specify on client letter? Is it Feb 2012 or 1 Oct 2012?
  
• My contract is till January 2013 but it will get extended. Is it compulsory to specify end date on the client letter?
  
• What other documents I will need for successful visa stamping?
  

Thanks in advance for your help.