The difference is in how the order was placed. Apparently the term "rough opening" was used when the term "jamb opening" should have been used. The windows, in all probability can't be returned as they would be a custom fit for the opening as stated on your order. The options as I understand this problem are; you could advertise the windows for sale and would only sell them one or two at a time over a long period, or, you could have your contractor take out the entire old windows and put new casings on them and re-install as the old windows were. At this point you should work out an new agreement with your contractor and strive for a reduced cost if he is at fault in his improper use of terminolgy. I hope this helps. Joel Kruskie, carpenter