An archive search of www.tvbarn.com yielded this information: NBC offered, among other properties, Concentration and Twenty One to the international market.

I'm aware that Concentration has been televised in the United Kingdom and Australia. Did Canada have its own version of the show, for people who didn't live close enough to the United States to get the NBC signal? Given the nature of rebus puzzles, exports of the Concentration format would have to be restricted to nations where English is the official language.

As for Twenty-One, was its format exported only to the United Kingdom? I've read that the U.S. and British versions of Twenty-One were very similar, in more ways than one!