I will make a small attempt, but will probably come up short, so others will correct me I am sure.
Prefixes:
F= 00/000/OM/Mini-Jumbo/Jumbo Shape, and slim acoustic electrics in later years.
D= Dreadnought shape (Martin Square Shoulder type)
G= Special variations
GF-Gruhn Era guitars
JF= 12 String Jumbos, same shape as the F
J= Jumbo
DV- Dreadnought Vintage series, same shape as D series
JV=Jumbo Vintage, same shape as F/J series.
A = OM sized (only 2 models)
CO/CV/CD=Contemporary Series.
Suffix:
NT=Natural (no color added to finish)
SB= Sunburst
AB=Antique Burst
C= Cutaway, Cherry finish
BL= Black or Blonde?
E= Electric or Electronics (has a pickup)
The C suffix can have different meanings on different models. A D40C is a D40 with a cutaway, but a D25C is a D25 with a Cherry (Red) finish.
All Dreads, with a few exceptions, are close to the same size. The F series 6 strings has different sizes, the F20 being the smallest, the F50 being the largest. Woods in the F series vary all over the place, sometimes you have guitars like the F47 (mahogany), F47M (maple) and F47R, all F47 size and shape, but with variaions in the back and side woods. You also get variations in models being applied. The all mahogany dread was originally called the D25, which went through a variety of changes, including change to a spruce top, arching of the back, and a variety of trim changes. But you also have all mahogany dreads that came later under the D15, D16 and D17 models. There are also some "slim" acoustic electrics, like the F65, which are slim guitars intended for stage use.
In the 12 string F series, the F112 and F212 are roughly OM sized 12 strings, with Mahogany back and sides, trim differences, the F312 is also OM sized, but of Rosewood
back and sides. The F212XL, F412, and F512 are full sized (17" lower bout) 12 sting Jumbos. The F212XL is Mahogany back and sides, the F412 is arched Maple back and sides, and the F512 is rosewood back and sides. The F612 is the super Jumbo (18" lower bout) rosewood 12 String (extremely rare). The F412 and the F512 were renamed to JF65 and JF55 for a few years.
The DV and JV series were more descriptive of a "voicing" variation/orientation than a shape. Guild seemed to want to re-voice their dreads to compete with Martin's equivalents (Guild DV6 or DV25=Martin D18, Guild DV52/DV72/DV73=Martin D28). I don't know much about the JV series, so you will need to wait for somebody to post on them.
There were two A series guitars, the A25 (Mahogany) and A50 (Rosewood), both OM sized.
The CO, CV, and CD are Contemporary series guitars, the CO and CV (CO with a Cutaway?) are OM sized, the CD is a dread. All of this series used a carbon fiber neck block (which has caused soem issues for some of the posters on this board), and were voiced for a more modern (=fingerpicking/fingerstyle) tone. This series was only made in Tacoma.
Like I said, I have probably left out a lot, and I'm sure other posters will be able to fill in the holes and make the corrections needed. Also, Hans, who is probably THE authority on Guilds will probably be along shortly to set us all straight.
One thing to remember is that Guild is very inconsistent with its model numbers, and has been throughout its history.
Kostas