H1 Approved for one month - Site visit, No Client Letter, Memorandum with dates

I have provided all the documents, instead of the client letter i have given a memorandum states that two or more years of contract in the xxx company, by the way, uscis had a site visit for my company before the decision was out. my question is
What is the difference between memorandum and a client letter?
There are no job duties and other details that the client mentioned about me, all it showed me my contract extended information? is that a reason I got less approval date? or what is the exact thing that USCIS did this?
But in my RFE, the field of work was given as 12/31/2019, so they told me to provide documentation regarding it, and I have shown them either.

Well, we really dont know what USCIS would look at in specific. There are many cases, where they have given shorter approvals, despite having documentation…they asked for a client letter with full details of the specialist work, etc. Your attorney would be the best person to analyse and then take an action on your situation. Discuss with them on the options.

So kumar , having a client letter with speciality work information will be a plus point

Yes, it helps. Read this experience and check screenshots here