I can only speak to one office so I shouldn't have assumed it was the case company wide. I only know two things:
1) At the office that my friend (who is also an interviewer) works, there is a pool that the interviewers collaboratively built and generally select from. They aren't required to choose from this pool, but 95% of them do because they contributed to it.
2) At MTV there's either a pool or the number of interviewers is so low that the same questions are repeated over and over at high frequency for several weeks, making it trivial to know which ones are likely to show up. I know because the questions I found on the sketchy Chinese forums were exactly the ones I encountered on my onsite interview.
As an alternative to 2, you just got lucky. There's lots of interviewers and lots of questions. My office is smaller than MTV, though not by much, and I don't think I've seen the same question come up more than a handful of times.
I'm unclear if 1 is referring to a specific office pool, which would be weird, or the global knowledge base I mentioned, but that has lots of questions, more than one could hope to memorize in any reasonable time frame.
So, there's a pool insofar as, like I said, there's a thing you're invited to add your questions to. But you aren't required to ask questions from the pool (and I know many people who don't). And also the "pool" is huge, which is different from some other companies I've interviewed at, where interviewers are required to ask questions from a small (~10-15), preselected set.
Problem with your approach is in order to make sure your made up problem isn't banned you have to go through all the banned question everytime you ask your question. That's a lot of unnecessary toil.
1) At the office that my friend (who is also an interviewer) works, there is a pool that the interviewers collaboratively built and generally select from. They aren't required to choose from this pool, but 95% of them do because they contributed to it.
2) At MTV there's either a pool or the number of interviewers is so low that the same questions are repeated over and over at high frequency for several weeks, making it trivial to know which ones are likely to show up. I know because the questions I found on the sketchy Chinese forums were exactly the ones I encountered on my onsite interview.