Jehovah's Witnesses, would it be accurate to say you celebrate the memorial once a year?

It's more of a commemoration than a celebration. It is a very solemn occasion and after listening to a public talk, the bread and wine are passed round but ONLY the "anointed remnant" (those who claim to be part of the 144,000 with a heavenly hope) may partake. Everyone else just passes the plate and the cup round to the next person.

They are not celebrating the death of Jesus, but remembering it. However, last year although 20,085,142 persons attended this annual event, a mere 18,013 Jehovah's Witnesses actually partook of the bread and the wine.