When nearing the end of year, it is quite common for this issue to occur. There a simple memory screening tests that your family doctor can perform that could then lead to additional tests if needed, but this would be a common place to start if you are concerned.

Probably not. If you have other memory issues, leaving the stove on, leaving the refrigerator door open, getting lost driving, unable to use a check book, then seeing your family doctor would be appropriate. But if the date error is your only concern, then I would not worry about it. Leon Rosenberg