Search Function Doesn't Always Work

I have noticed that the boards advanced search function doesn't always work. In particular, I have been trying to find all threads started by a certain member, and know for a fact that not all these threads are being found. Anyone know why?

Is the member you're searching for a Jr. VIP or higher? If so, that could be why. There is a Jr. VIP forum that does not show up, unless you are one.