The koolaid WT issue for February has an interesting article about when your baptism can be considered invalid.
But the main thrust of the article is aimed at making it super clear that if you were present at your Bapt. talk and answered the two questions then forget about it, elders are put on notice to not let anyone off the hook.
But... If you were committing a serious sin and hid it at the time of your baptism, then it was invalid, and point is, they'd still announce you not being "one of J.W.s" so if you plead your case to walk away from the WT saying you didn't know what you were getting into, it will do no good, but it will be grounds for an announcement.
Just Ol' Mother WT tightening up loose ends.