What happened to the "19"?

I was born as WWII started so I was alive for more than 40 years during the time when the calendar number for the year always began with "19".  Now it doesn't!!!  For goodness sake, will they make up their mind?

How many ruined checks and notes do I have to suffer?  Then, I suppose, once I am finally used to "20", it will be "21" or some other number.