This alley ran from #144 S. 3rd to #79 S. 4th, according to the 1823 directory. It does not appear as such in the 1785 directory. The 1796 Prospect says of it: "Runs East and West between Third and Fourth-streets, and between Spruce and Union-streets-- is about 20 feet wide, and 396 feet long." It still exists, and some early houses still stand on it.
There are no matchups between the 1791 and 1796 listings. The alignment between them is entirely based upon the one house number we have for the 1796 Prospect listings, #10, and the fact that they were listed in the order they actually existed. The fact that there were exactly three houses before #10 and that this matches up with the 1791 listings, definitely helps support the alignment.
(1791) #1 Cypress Alley, Berry, Mrs.
(1796 Prospect) [no number then affixed to house] William Adams, Stable-keeper
(1791) #2 Cypress Alley, Stewart, William.
(1796 Prospect) [no number then affixed to house] James Morrell, Mariner; _______ Sink, Carpenter
(1791) #5 Cypress Alley, Cross, Katharine
(1796 Prospect) [no number then affixed to house] Dunkin Campbell, Shoemaker
(1796 Prospect) #10, Charles Mahy, French citizen
(1791) #12 Cypress Alley, Hellings, John, accomptant
(1796 Prospect) [no number then affixed to house] Phineas Stretcher, House-carpenter
(1791) #14 Cypress Alley, Campbell, Mary, boardinghouse
(1796 Prospect) [no number then affixed to house] Thomas Stretcher, House-carpenter
(1791) #16 Cypress Alley, Mason, Philip, carpenter
(1796 Prospect) [no number then affixed to house] James Little, his School-house, three
grand apartments, in one of which a Book Auction is often held-- With the help of two
assistants Mr. Little teaches 150 scholars.
(1796 Prospect) [no number then affixed to house] Robert Hopkins, Inspector of the Port
(1796 Prospect) [no number then affixed to house] Joseph Burn, Woolcomber
(1796 Prospect) [no number then affixed to house] Thomas Smith, Shopkeeper
(1796 Prospect) [no number then affixed to house] William Mulhallan, Shoemaker
(1796 Prospect) [no number then affixed to house] Reese Evans, Carpenter
(1796 Prospect) [no number then affixed to house] Thomas Webb, Mariner