I don't know what you mean by EOOW letter. When I qualified, the only documentation I had was a service record page 2 entry, my evals, my end-of-tour, and the biiiillllllions of engineering log entries. That being said, I am also at a loss as to why they are asking for it. I never was asked for proof, not that this helps you any.
Do you not have the page 2 or eval to provide proof or is your potential employer wanting more?