Yeah, it happened to two of my friends. One of my neighbor took 3 years sign language lesson and I have been helping her with her "homework." When she got married and she got busy - 6 months later, I finally saw her and she already forgotten some of sign language. She was able to read my signing, but now she asked me to slow down - at snail pace.
Other friend, he told me he took classes, but already forgotten when I met him. Since he's co-worker and I will feed him some sign language to see if he will remember them.
