As I understand it, Start and End date are set the same so the data looks clean. Copyright was given in that year… and lasts as long as laws in relevant area.
Bit like when something is recorded on a specific date we also copy the value into start and end boxes.
That’s the guideline 
The reasoning is that we have no data about who owns the copyright at any given moment, these are sold, exchanged, merged and repackaged all the time, so just storing what we know for sure (“this release had this date”) is safest.
Ah, I see, thanks! It looks slightly odd in the editor, but that makes sense.