Lots of divers take a refresher course after a year off. I taught many a class. Some of them really needed it; some of them didn't. Other people who feel confident in their skills just rent pool time from a local shop.
It is surprising what you can forget. I once did a refresher for a smart, well-educated woman who had been diving for years and had only taken one year off. I was surprised she felt she needed it. She had all her own gear, and when she set it up and turned on the air, she looked at her air-integrated computer and said aloud that it had successfully analyzed the gas in the tank as 32% nitrox. Say what? I had a tough time convincing her that her tank had just plain air in it--her computer had been set to 32% on a previous trip, and it was not reading the air in her tank. She had to do that analysis separately and then set the computer accordingly. She was absolutely convinced her computer was able to analyze the gas in her tank.
It is surprising what you can forget. I once did a refresher for a smart, well-educated woman who had been diving for years and had only taken one year off. I was surprised she felt she needed it. She had all her own gear, and when she set it up and turned on the air, she looked at her air-integrated computer and said aloud that it had successfully analyzed the gas in the tank as 32% nitrox. Say what? I had a tough time convincing her that her tank had just plain air in it--her computer had been set to 32% on a previous trip, and it was not reading the air in her tank. She had to do that analysis separately and then set the computer accordingly. She was absolutely convinced her computer was able to analyze the gas in her tank.