The synagogues to be added are listed in the directories starting in 1869 and go to 1933-4.
What's helpful on these lists -- besides the synagogue name and its address at the time the directory was printed-- is that often times the rabbi, president, reader and sexton of the synagogue are listed.
I have amended the way I present this particular list, so that it is an "address directory", so to speak, so it will be most helpful if you knew at least the street on which the synagogue once stood. Of course, you can always do a search on the page for any keyword you choose.
I will notify those of you who follow my blog once the webpage is updated, though as I've said, it might take a few weeks or so. To see the current lists of New York City synagogues, click here.