They are in neat cubes, except for the hand-placed sectors. Move the pointer a long way from civilisation, zoom out to a high level and move along the galaxy map along one of the axes and you'll see. You can follow the lists along and find repeating patterns. If you like and find a sector called AlphaAlice, the next sector along will be AlphaBob, the next sector AlphaCharlie, then AlphaDave... and so on. Except that sometimes the pattern breaks and you see something like AlphaAlice, AlphaBob, Beta-MaxChuck, AlphaDave instead. Within each cube you get all the suffixes "AB-C" and, uh, sub-suffixes "a1-1." I haven't looked in detail as to how the placement of these suffixes relates to the overall position in the bigger cube of the sector, but they can be quite widely spaced IIRR.
An interesting thing for me is the correlation between AA-A suffixes and high-mass systems.