OEM products are manufactured by the original printer manufacturer. They are in the factory sealed boxes and have the manufacturers warranty.
Page Yield is an industry standard based on 5% ink or toner coverage per 8.5x11 in. page (see 5% page yield example here). Page Yield is an approximation and fluctuates according to individual use. Users should expect coverage to increase 15%-100% and Page Yield results to drop when printing large text blocks, graphics, photos, illustrations, web pages, etc.