I would scan or copy the postmark and the letter itself--my experience with Disablity is that they want documentation out the ass for everything--but as I found in my case, that documentation )in my case, the doctor changing his mind,needing CAT scan, etc) tipped the balance on my side. As far as caseworkers, I ride their asses, call 'em, bug 'em, fax 'em--that's what made the difference in my specific case, although your experience may be different...but I am sending positive mojo your way!!