H1B Documents Clarification

Hi All,

Iam a new H1B applicant for FY2021 from India Working for a IT concern for last 1 year…
Prior to that i have worked with another IT concern for 8 years.
Now my new employer has put on H1B nominations for me and it got selected in lottery.
I have a doubt on the experience letter which i need to file in the document… Is the experience letter mandatory? My previous employer has given me Separation Letter with date of joining and date of relieving… So is that document alone is enough?
The reason why Iam unable to get Experience Letter now is my previous employer is facing some malware attacks. So they are also unable to send me any experience letter now…
Is my Separation letter alone is enough for the Document submission or should i get exact Experience Letter??

But when i file my document in Internal Portal of the organization the previous experience letter is mentioned as not mandatory… I am confused now to get this document or dont have to care of it?

Can someone please assist here??