The initial Mail Classification Schedule shall specify the market dominant and competitive product lists. The Mail Classification Schedule product lists shall reflect the market dominant and competitive product lists identified in 39 U.S.C. 3621(a) and 39 U.S.C. 3631(a) respectively. The explanatory detailed descriptive information specified in Sec. 3020.13(a) and Sec. 3020.13(b) shall be incorporated by subsequent rulemaking.