A cacher named MAGICN3 messaged me about this challenge, it was showing only 25 states found and need 26 states (including DC) He has found two caches that geocaching.com says are in DC but project-gc does not :
GCF40C Northern Most Corner
GC1B284 Cache for NE-one
These are at the D.C. Boundary stones so they are really close to the line. Perhaps the polygon definitions need updating?