• Technically, they were called Proficiency  Badges.  Girl Scout Proficiency Badges have long been a mark of a Girl Scout who tested herself and passed. It was expected that a Girl Scout in uniform and wearing badges proudly on her sleeve, be able to answer any question or perform any skill that she learned in the effort to earn that badge at any time.
•  Over 200 badge designs have been used since the beginning of Girl Scouting, always updating the skills to meet the needs of a Girl Scout in a changing world.
• Lion Bros. Company of Baltimore, Maryland has been and still is the exclusive manufacturer of Girl Scout Proficiency Badges (thank you Julie Ward for this info!).
• Ages and dates for badges are general. Badges were produced as they were needed and for this reason not all badge designs can be found in every fabric for their time period. Popular badges would have sold well and therefore been crafted frequently enough by the manufacturers to be in all the fabrics during it's time. Being thrifty, Girl Scout shops would have continued to sell the less popular badges in older fabrics until supplies were deleted.

Badges are dated by the fabric and by the design:

F = Felt with embroidery 1913-1918
K = Khaki fabric, 1918-1928
GG = Grey Green fabric, 1928-1938
SG = Silver Green fabric, 1938-1948
BMG = Bright Medium Green fabric, 1948-1955
ME = Bright Medium Green fabric with finished "Merrow" edge, 1955-1960
LG = Light Green fabric, 1960-1963
LGJ = Light Green fabric, Junior Girl Scout 1963-1980
LGC = Light Green fabric, Cadette Girl Scout 1963-1980

F = Felt with embroidery 1913-1918

Generally, felt badges were white felt with blue embroidery. This coordinated well with the blue uniforms of the day. There are a couple of exceptions; red felt was used for the 1913-1916 Ambulance badge and blue felt was used for the 1913-1918 Hospital Nurse badge.

K = Khaki fabric, 1918-1928

The change to a khaki fabric for uniforms also brought a change in the production of badges to khaki (K) fabric in 1918. Briefly they were produced in blue embroidery thread, but this quickly changed to black. The designs remained the same as the white felt, however the fabrics used varied in color and thread - olive drab, speckled brown & white and a twill. The update of 1920 standardized the fabric and brought design changes. Today these badges come in many shades due to time, aging and early laundering techniques.

GG = Grey Green fabric, 1928-1938

Grey Green (GG) fabric was introduced in 1928, a mixture of greyish green and white threads. Badges continued to be produced on squares of fabric for the Girl Scout to trim and tuck when sewing them on her sleeve, or to leave as a square. By 1933 all badges were produced as a circle with fabric edges. Designs continued to be introduced and deleted to keep up with the modern world.

SG = Silver Green fabric, 1938-1948
1938 brought an explosion of designs, up to 109 with the change to the new Silver Green (SG) fabric of blue and white threads. However - it is known that discontinued GG designs were produced on SG fabric, increasing the number of badges to be found.

BMG = Bright Medium Green fabric, 1948-1955

ME = Bright Medium Green fabric with finished "Merrow" edge, 1955-1960

The last of the badges to have a fabric edge was the Bright Medium Green (BMG) dating from 1948 to 1955. Manufacturers began to trim the edges of the badges with embroidery thread in 1955 and the excess fabric was no longer needed. These badges were on the same fabric but with a Merrow Edge (ME). Most badge designs moved from BMG to ME and can be found in both styles. Only 2 designs were not made in BMG and just a few were retired before the ME.

LG = Light Green fabric, 1960-1963

The introduced of the new Light Green (LG) fabric in 1960 retained all the ME designs.

LGJ = Light Green fabric, Junior Girl Scout 1963-1980
LGC = Light Green fabric, Cadette Girl Scout 1963-1980

However the program change in 1963 that split the Intermediate program into the Juniors and Cadettes had a big effect on the badges. Many designs remained, but the Cadette badges were offered with a yellow border. Junior badge designs that remained looked exactly like the LG badges. Dating these badges becomes a matter of studying the backing material.

(brown border due to scanner, it's really green)
Although the designs remained the same in 1974, the fabric used for Junior and Cadette badges changed from a LG to a fine pinstripe (PIN). In 1978 the fabric changed again to a Vivid Green Twill (VGT), and marked the first time a badge fabric not used in the making of the uniform since the white felt badges.