The factory eventually standardized their nomenclature in the mid '90s, using the below pattern. The 3rd digit determines the action, with 4, 5 and 8 signifying DAO models.
10xx 10mm
22xx .22 rimfire
39xx 9mm single stack
40xx .40 caliber
45xx .45 caliber
59xx 9mm double stack full size
69xx 9mm double stack compact
xx0x TDA full size
xx1x TDA compact
xx2x Frame decocker full size
xx3x Frame decocker compact
xx4x DAO full size
xx5x DAO compact
xx6x TDA mid size
xx7x Frame decocker mid size
xx8x DAO mid size
xx9x Non standard combination
xxx3 Alloy frame silver
xxx4 Alloy frame black
xxx5 Steel frame blue
xxx6 Stainless steel frame
xxx7 Non standard combination
Not every model was put into production, and some only in limited numbers. Some early guns just used the original model number with DAO on the end (3914 DAO), while the econoline would put a D on the end (457D).
Hope this helps.