Work Experience Letter for past 10 years

Regarding the subject matter I seek advise from the expert members of this forum, I have been working in an overseas company for past 6 years and for this my employer has issued an experience letter + salary letter (both). However for the ex-employers I don't have any information about those companies whether they still exist or not. Or they might be merged with some other company. In any of the case after such a long time it's not possible for me to approach my ex-employers and ask for experience letters. All I have is a photo copy of experience letter for past one of the employer out of three. Now I am really confused how I do can cater CIO with old experience letters. I really need you expert advise on this issue.
Last but not the least; the current 6 years experience letter that I have from existing employer is only describing my; job title, service period and monthly salary whereas following information as required by CIO is missing from certificate and my company is not willing to depict these points in their letter. They just follow their standard format.

I). Total number of hours worked per week.
ii). Main duties and responsibilities of job position held by me.
Please reply.

Regards,
Aayan