score:1
You should never lie and always cooperate by giving all relevant documents and information (and an overstay is a relevant piece of information).
I left Spain quickly and voluntary
What did the Spanish say when you left
For important matters, information is exchanged between the countries.
Telling them the worst, discribing the situation as you have done here and let them deside how important it is, is better than them finding out later that you deliberately left out relevant information.