Some addenda to the list:
Alleys can split off into sub-Alleys, such as the Non-Hemalurgic Research Division.
Any Alley whose prime factors include 43 and 97 is flat and restricted to the second dimension.
Relativity is much more prevalent in odd-numbered Alleys due to a slower (or is it faster???) speed of light.
Time passes much faster in some complex-numbered Alleys than in others.
Alley 42 harbors the Answer to the Ultimate Question of Life, The Universe, and Everything. Alley 42i harbors the Question. Both are off-limits to all but Adonalsium, the Superb Goose, Mr. Dictator Regent of All Creation, and other supreme beings.