It's possible that the spacers (washers) were used because the chainring bolts are too long like blakcloud said. The other option is that the spacers were used to adjust the chainline by bringing the chainring further or closer to the frame than the normal position.

I would recommend to visually inspect your chainline with the 3 options and pick the one which gives you the straightest chainline. Try to place your chainring in a position so that an imaginary line in the plane of your chainring bisects the rear cassette in the middle of the cassette like the diagram attached. That's probably the best place to put your chainring.