Tele,
You are thinking like a Catholic. Of course they wait in vain, in the sense of salvation, because the Messiah already came for that purpose. We all know this.
The Congregation is saying they do not wait in vain in the sense that their Messiah IS indeed coming. Just not who they expect or for the purpose they expect. What these ecuмenical statements deliberately leave out is precisely the "significant silence" Vennari pointed out.