Another way to recognize a longcoat is by looking at the hair on the backs of the ears. As Dee Cee mentioned, at about six (6) weeks of age it is easy to spot.
There are two (2) types of longcoat. First-the type referred to as "long stock hair". This hair is longer than normal, but the dog/bitch does have a true undercoat, and can be eligible for a breed survey result such as Kkl-2, rather than Kkl-1.
The second type is a true "longcoat". This hair is longer than normal, and the dog/bitch never develops an undercoat. A coat of this type will not pass a breed survey.
In all cases, the dog can be registered and trained just as any other dog. Certain lines produce the longcoat, but both parents must have the recessive gene for this to happen.