Later, the quality levels were defined with A, B, C and D instead of 4, 3, 2, 1, because thenumbering is in reverse order to other GE standards and public standards, which could lead tomisunderstandings.New documents shall always use the new quality level designation A, B, C or D (as introducedwith revision D of HTGD620179). But the old designations (HTGD620179 until revision C) canremain in older documents, as a mixup with the new designation is not possible