When printing on the reverse side of NCR pages, remember that a perforation on the left or right side of the page will flip on the back side. If there is a 15mm margin for the perforation on the left-hand side on front side, the back side will have a 15mm margin on the RIGHT hand side.
NCR paper stock is usually 60gsm and somewhat transparent, so if you want to print on both sides of the stock be conscious of the appearance of ink through the stock.
If you are printing terms and conditions on the back side of an NCR page, consider using a lighter ink so it is less visible from the front side.