Xnnnn.yyll
       ^  ^   ^ ^
       |  |   | |
       |  |   | +-- letter(s) used to designate individual items
       |  |   |        of a single system/donation
       |  |   |
       |  |   +-----year, 4 digits if post 1999, else 2 digits
       |  |
       |  +---------accession number
       |
       |
       + prefix
          X   - museum collection
         XB   - Bell collection, donated to museum
          B   - Bell collection, (willed to the museum, 
                      but not donated as of now?)
         XD   - Initial Dec Museum collection
          L   - Loan