How accurate is it to measure what has not happened in the future?

Can't compare, eight characters to see the overall fate. For fortune telling, there are many prediction methods, such as Heluo number, four-column prediction, Wei Zi number, iron plate number and so on. Six hexagrams can also tell fortune, but they are rarely used, that is to say, they are not targeted and are not specially made for fate.

Six hexagrams is one of many forecasting methods, which can be calculated from astronomy, geography, personnel and other aspects.

If it is fortune-telling, personally, the prediction method specifically for fortune-telling will be better. As for authority, I can't say. The six hexagrams you mentioned were invented by Fang Jing in the Han Dynasty, right? You started divination with copper coins, and you asked the fortune teller to shake it himself?

There is a saying that it is easier to start divination than to break it. In the eyes of top experts, the methods are just different paths. As long as the skills are sufficient, I believe that different paths should point to the same forecast trend.

However, such masters are rare. I'm just a fan of Yi-ology, and all the above are personal opinions. I hope it helps you.