"Mabel and Albert" and their family lived in our house for more then 30 years. Sadly Albert died and then quite a few years later Mabel died at a ripe old age. We bought the house nearly seven years ago from her children.
Every year since we moved in we have received a posted Christmas card to 'Mabel and Family' signed x and y (but no return address). Obviously they've not had one off Mabel in the last seven years ...
We've just received this year's card 
So, seriously, how long would you keep someone on your Christmas Card list if you hadn't heard from them? A year? Two? Seven???