Not an answer but an idea:
Considering the hint "You can only add 2 numbers at the end at the moment. But if you take too much time to solve this, you may have to find more..." and the knowledge tag, I suspect that the answer has to do with occurrences of something.
7 occurrences are listed, and we can only list 2 more (at the moment). Therefore we are looking for something that has happened 9 times...
Those numbers could represent dates, or could encode information about these events in some way.
Although this idea hasn't gotten me anywhere yet, I'm thinking things like comet appearances, presidents... but I can't really get anywhere without knowing what kind of knowledge is needed.
Edit:
However, looking at the 1st hint, it says we cannot be sure about the answer, although we can about the 1st part of the pattern. Perhaps this means 7 occurrences have taken place, whilst the 2 we can put for the answer are the next ones predicted which have not happened yet, and we aren't able to predict any more (for whatever reason).