She mentions at one point that she had only had one wrong viewing before. Another time she mentions to Rand that her viewings of Moiraine did not come true. She mentions the viewing that Rand would fail without Moiraine while she's watching him get ready to visit the Cairhienin rebels in aCoS, feeling guilty about lying to him when he asked her earlier what viewings she hadn't told him about (she responded that she had only kept back one - about him touching another man and they merged and one dies). She is feeling guilty because she only told him about the one, but justifies that by thinking it would serve no purpose to tell him about the viewing that he would almost certainly fail without a woman who was dead and gone. The part where she only had one viewing that was wrong was in a completely different context.