In AKC, I think GSDs are all shown as one "breed," unlike collies that can be shown as smooth or rough. In the SV, they are two separate types (stock and long coat).
I have a SV registered long coat so I have been trying to understand the specifics (just out of curiosity). From what I understand the SV has two coat types - Stockhair and Longstockhair with undercoat. Longhair without undercoat is considered a breed fault, not acceptable for breeding.
Prior to 1999, longstockhair with or without undercoat was a breed fault.
From the 2013 SV Rules for Breeders and Breeding -
"This breed, the German Shepherd Dog, is allowed only two varieties of “Haararten” (coat types):
(1) straight-hair, medium-length topcoat, and (2) Langstockhaarigen (longcoat with woolly undercoat present).
Breeding the harsh-short-coated (normal) with longcoated dogs is not allowed. Dogs from such combinations
can be allowed no entry in the studbook or supplemental registries (Anhangregister). Breeding such dogs is
only allowed with others that are registered as being of the longcoat variety. "
I thought I saw some recent SV rule changes about about longcoats, but can't find it now...
From schaferhund.com - Breed standard
The medium smooth coated German Shepherd Dog - The outer coat should be as thick as possible and composed of straight, coarse hairs that lay close to the body. The coat is short at the toes, but it grows longer and more profuse on the neck. The hair grows longer on the back of the fore and rear legs as far down as the pastern and the hock joint and forms moderate trousers on the thighs. The length of the hair varies and due to these differences in length, there are many intermediate types. A too short mole-like coat is faulty.
The long smooth coated German Shepherd Dog - The individual hairs are longer, not always straight but definitely not lying close and flat to the body. The coat is considerably longer inside and behind the ears, on the back of the forearm and usually in the loin area. Often there will be tufts behind the ears and feathering from elbow from elbow to pastern. The trousers along the thigh is long and thick. The tail is bushy with light feathering underneath. This coat type is not as weather proof as the medium coat and it is therefore undesirable. However, if there is sufficient undercoat, it may be passed for breeding. Dogs with long coats are commonly narrow chested and have narrow over stretched muzzles. The dog with sufficient undercoat may be passed for breeding, depending upon the rules and regulations of the country.
The long coated German Shepherd Dog - The hair is appreciably longer that that of the long smooth coated dog and tends to form a parting along the back. If present at all, the undercoating will not be weather proofing nor of utility value and, therefore, should not be passed for breeding."