question Approach0 can find formulas appearing in questions or answers, but no in comments. Is that correct?

I have tried searching for $\sum_{n=k}^{\infty} \frac{1}{\binom{n}{k}}$, which appears in some comments.

@MartinSleziak You are right. The reason is perhaps I was desperately trying to finish a prototype that was supposed to be just working, I was avoiding to write a few lines more code to further crawl comments at the time dated back to when I was writing the very first version of crawler. So, do you think it will be better if we also crawl comments?

Well, it's not that easy to say.

Examples of the comments I linked above are of the form: "look this would also work for this more general sum".

So I am not sure to which extent would the question be considered relevant among search results for this formula.

However, the two formulas are simply different notations for the same thing.

Or $n!$ can be written sometimes as $1\cdot2\cdot 3\cdots n$ and sometimes as $1\cdot2\cdots n$.

I guess that it is not difficult to come up with various examples of mathematical expressions which can be used to denote the same thing but written differently.

There is a chance that in some cases one of the reformulations can be found in comments but not in the question.

@WeiZhong I do not have clear answer to this. There are many comments which point out that the original question can be generalized in some way. (But the same thing probably happens with answers sometimes.) One of the question to consider is whether you want to include such situations.

But I am glad that at least you confirmed that it works with comments the way I thought. (Based on the above experiment.)