In Australia, where I live, it said "Tamagotchi Connexion" on all of the shells until the second or third wave of v3s, when they started writing just "Tamagotchi" on them. Then, when the v4s came out, they no longer wrote "Tamagotchi" on it. Sometimes they wrote "TMGC" (they did it on the Mametchi and Kuchipatchi designs, not sure if there's any more) but that's all I can think of. The v5s also don't have anything written on top of them. But some designs do have writing on them- for example my Tamagotchi has "Bagubagutchi," "Chitchi," "Hanatarezoutchi" and "On Sen Moguratchi" written on it.
Starry_Sky, 2004 is when the first Tamagotchi Connexions/Connections came out, so maybe that's why they still say 2004 on them? Though they first came out in November 23rd 1996 in Japan, and in May 1997 in other countries.