Fall adult dowitchers in worn alternate plumage are hard to identify. An article by Lee and Birch in Birding, Sept. 2006, has lots of tips on separating them: http://www.americanbirding.org/pubs/birding/archives/vol38no5p34to42.pdf . One new suggestion they make is that the shape of the dark parts of the scapulars and greater and median coverts can be decisive -- those of Short-billed are V-shaped, of Long-Billed are squared off. Here are three dowitchers I photographed at Palo Alto Baylands on August 2, which have visible examples of these feathers. The distinction based on bars (LB) vs. spots (SB) may help with these as well. (Note all three of these are into molt, at which point, Lee and Birch tell us, the most familiar distinction, based on extent of white on the underparts, loses reliability.)