What is the law of Chengdu Mahjong "5 123", or "composite board"?

In the era of playing mahjong in hand, a player once discovered a rule of "5 123" according to the rule of dice rolling, which is also the "combined word card" as the saying goes in Chengdu. However, this is a loophole in grasping the rules. If you get caught, you can only blame yourself for your limited knowledge. Later, in Chengdu Mahjong Rules, the dice were rolled by "taking the smallest", which changed the basic law of licensing, and "5 123" became history. It can be seen from this example that perhaps every rule reform of "bloody battle to the end" has its inevitability.