Interesting recap today in WSJ about how National Enquirer nailed the truth about Senator John Edwards. http://tinyurl.com/ylguxvr
Sometimes as CI professionals you get in this "I told you so" situation. Your customer doesn't believe you and perhaps even publically eviscerates the argument you present. Been there?
1) If it's material to the success of your organization, remind that you are of a different opinion and go about your business. Continue to probe and gain additional confirmations using all available means. If it's not material move on. You won't be right all the time and everyone knows that.
2) Identify, engage, equip allies in your organization and network to help find the truth. Be at the right events, follow the right news nodes/forums, call on the right customers, ask provocative/ballparking questions to people closest to the action. Your real investigative team is probably still pumped...just like at the Enquirer.
One time I needed pictures of the newly produced item being loaded into a truck to nail the case. (no, no trespassing was involved)
3) Build part of your intelligence effort around addressing the biggest objections of the naysayers. Compare those closely to the assumptions vs. data which will condition you being correct. Work quietly until you have it nailed. Stick to the facts and most plausible scenarios cognizant always of competition's financial & marketing models & relationships.
4) Use overwhelming force to make the case a final definitive time. This could be a critical meeting where the decison will go one way or the other depending on your information. It could be use of SM and the rumor mill of your organization. It could be jumping ranks over the normal chain of command to the person most at risk/reward if/when you are right.
Hope you win your "confession".