People were deluxifying these cars almost from the day they were new.It could have happened at any time in the last 95 years.Side mount spare should have a full width bumper on the rear.Dealers would do about anything to sell a car though.There wasn't much reason to make a standard over to a DeLuxe in 31,as there were only a handful of Standards made in that year.I think it was somewhere around 5000.Most were DeLuxe.Look to see if the spare tire socket is bolted or riveted to the frame.Not many Standard roadsters missed the deluxification routine in the 50's,60's,70's and 80's.Do you know the history of your car back to say,the war years?