General Information

Most Gibson mandolin models are comprised of a letter prefix and number suffix. The letter indicates the body and mandolin style and the number indicates the features/appointments (however there doesn't seem to be a standard scale with the exception of 1-5 i.e. A model 5 is better than a 1, but also better than a 40 or 50).
Early models produced until 1908 were not built that well and are not viewed as collectible as later models. Mandolins get consistently better through the 1910s and 1920s when Lloyd Loar came to Gibson as an engineer in 1922. The mandolins (and other instruments) produced during his tenured are some of the most collectible models ever produced. The Gibson F-5 from 1922 to 1924 is easily one of the top ten all-time valuable instruments. Gibson produced less mandolins in the late 1920s and 1930s due to lack of demand, but quality also tapered off during this time. Mandolin production was suspended during WWII, and any mandolins produced after this are worth significantly less than pre-war models. While Gibson has produced at least one mandolin since the early 1900s, the quality never came back to the 1920s standards until the late 1980s and 1990s when production moved to Montana. Price lines reflect the general quality of construction and sound and can be seen in the individual model listings.
Model Prefixes:
A - Typically used with symmetrical body-shaped models.
C - Used on the Army and Navy Special.
EM - Electric mandolins
F - Typically used with the two- or three-point body shape. This is the original Gibson mandolin body shape.
H - Mandolas
J - Mando-Basses
K - Mandocellos
Here is a list of the various designs that happened over the years.
1890s-late 1902 - Models were made by Orville Gibson before the Gibson company was formed in late 1902. These models typically feature a wider and deeper body.
1902-1904 - Models feature the Gibson company logo but are still Orville Gibson style mandolins.
1904-1907 - Features now include a curved back, a separate neck from the sides, no volute on the peghead, and The Gibson logo becomes standard by 1907.
1908-1909 - Body becomes more narrow and shallow with some birch back and sides, and a higher bridge and elevated pickguard are introduced.
1910-current - The two-point body shape is introduced on the F models.
Circa 1922-1924 - Lloyd Loar is chief engineer and responsible for designing most models during this era.
Circa 1926/27 - Maple back and sides are introduced on all models.
1942-1946 - No production because of WWII.
1984 - Production moves to Nashville, TN from Kalamazoo, MI.
1987-1997 - Production is moved to Bozeman, MT.
1997-Present - Production is moved back to Nashville, TN.