They have to relearn the task to how a 'lefty' or a 'righty' might do it. We've discovered that many great products are no longer being manufactured. It has nothing to do with the quality or usefulness of the product. The discontinuation has more to do with business and finance. For example, we've seen products that took too long to be sold, so they were discontinued - when the problem was probably with the marketing of the item.
Some manufacturers are very small and are simply no longer in business.
Other great items simply cannot be manufactured at a reasonable price. For an alternative to a calendar, use an erasable white board to write the day and date in large print and place it in a highly visible location. Some people also like to draw something to indicate the weather outside, like a sun, rain drops or snowflakes. My Dad is using a walker and keeps bumping into the door as he moves from room to room. Offset hinges are the answer.