How’s this for a stretch:
The game (or game name) involves something along the lines of “Truckin’” or “Grateful Dead.”
How I got there:
If the first two numbers are latitude/longitude and point to Copley Square and the Trinity Church, it could be a reference to the movie “National Treasure,” in which the treasure was beneath Trinity Church.
Now, it was mentioned that the third number could be a Dewey Decimal system number and that the Boston Public Library is near Copley Square. 342 in the Dewey Decimal system is constitutional and administrative law, strengthening the connection to “National Treasure.” However, it was also stated that the Boston Public Library uses the Library of Congress system (I can’t find that stated on wiki, but I’ll take your word for it).
Searching “national treasure” on Wikipedia yielded a page about national treasures instead of the movie. Listed was a song called “Truckin’” by the Grateful Dead, which is considered by the Library of Congress to be a national treasure.
The chorus of “Truckin’” runs like this:
Sometimes the light's all shining on me
Other times I can barely see
Lately it occurs to me
What a long strange trip it's been
(Yes, I know this is entirely crazy. I just had fun linking it all together, and it’s a really odd set of connections.)
Link to lyrics for “Truckin’”
Link to the wiki page on national treasures in general.
Link to the wiki page on “National Treasure” the movie.