"New" Element Property?

 I am having a bit of confusion as to what constitutes a "New" element in the element properties. Lines that were just created in a brand new file are considered "Not New," while a line from a file created nearly 2 months ago is still considered "New," even after it has been modified. I checked the help documentation, but there doesn't seem to be any indication in the element properties page as to how it's determined. I'm hoping to find a way to have another party make additions or changes to an existing file and then isolate the differences by whether they're considered "New" versus "Not New."