At least part of the answer to this query is that when Georgetown officially became part of Washington, they were required to change the names of most of the streets in Georgetown. This was about 1870, if memory serves. The name changes were, shall we say, not exactly creative, but thought necessary to bring Georgetown into the L'Enfant street grid of the rest of DC. Congress Street, for example, became 31st Street NW. Montgomery Street became 29th Street, etc. The same is true with the cross streets. Dumbarton and Prospect kept their names, but most of the other Georgetown street names were changed. I have a list of the old street names and what they were changed to, if needed. Jane Donovan