The fourth digit seems to convey the following meanings:
0 = Magazine disconnect, internal lock, standard sights
2 = Magazine disconnect, standard sights
3 = Standard sights
4 = Magazine disconnect, internal lock, night sights
6 = Magazine disconnect, night sights
7 = Night sights
The first digit distinguishes between LE (3; three full-capacity magazines), civilian (2; two full-capacity magazines), and civilian-restricted (1; two ten-round magazines).
The sixth digit indicates caliber:
0 = .40 Auto
1 = 9mm
2 = .357 Sig