Received RFE for job duties letter from current and previous employers

I have received following RFE:-

1.Letter from current employer confirming progressive employment in the organization since I first joined, which should include a breakdown of every position I held; for each position, include (a) job title, (b) dates the position was held, and © detailed job duties

2.Letters from all previous employers, that includes for each position held: (a) job title, (b) dates of employment, and © detailed job description. As the letters previously provided do not contain any job duties.

I have total 15 years of experience in IT. I am working with my current employer for more than 11 years. I have all the details available to respond RFE related to my current employer. i.e. point 1.
However, I cannot provide the letters from my previous employers as those firms are closed/ merged into other originations.

Please suggest alternative/s to respond the REF for previous employer’s job duty letters.

Will the letter for my current job suffice as I am working with my current employer for more than 11 years?