Year

You might enter any year in the release year tag but it is only written into the song if the value is 1900 or higher.

The earliest known invention of a phonographic recording device was the phonautograph, invented by Frenchman Édouard-Léon Scott de Martinville and patented on March 25, 1857. It could transcribe sound to a visible medium, but had no means to play back the sound after it was recorded.

Thomas Alva Edison conceived the principle of recording and reproducing sound in 1877 as a byproduct of his efforts to "play back" recorded telegraph messages and to automate speech sounds for transmission by telephone.

1900 is a bit to high as a lower limit.

Year null

Once a year has been entered WMP wants a number (=> 1900). You can't clear the field.