B-grade simply refers to media that is not up to the top factory standards. Depending on the media brand, it can mean anything from total crap to very good media. In the case of TY, B-grade is often no different than A, but there’s no way of being sure until you get it. The TY has also been called “Value-line” by several sellers. Mostly it’s just old stock, but can also include lower quality stuff. With other makers, the terms are less meaningful because their A grade is crap to start with. TY Value-Line 4x has also included G02 as well as G01, (so you don’t always get G01 even though it’s sold as 4x). If you get G02 and have a 4x burner, you may not be happy with the results, so you would want some assurance from the seller that you will get G01. If you have an 8x burner, you should probably just pay the price for A-grade G02.