Pentangeli's survival may have gone public before Fredo met with Michael in the boathouse. But, Fredo knew that Questadt belonged to Roth--and that wasn't public. Why didn't he tell that to Tom before he met with Michael?

We saw the depth and intensity of Fredo's resentment of Michael in his outburst at the boathouse. It was pure hatred. He could have helped his brother by telling Tom about Questadt (and Pentangeli) before Michael testified. But, he wanted to hurt his brother by waiting to reveal what he knew until after Michael perjured himself.. It was Fredo's vengeance for being passed over and for being treated as stupid and as a go-fer.

I posted years ago that Fredo was far more involved with Roth and Ola than he let on. That's how he knew that Questadt belonged to Roth:

http://www.gangsterbb.net/threads/ubbthreads.php?ubb=showflat&Number=472494&Searchpage=1&Main=16944&Words=%2Bconspiracy&Search=true#Post472494