Russia claimed to have no involvement in Crimea (later admitting they had); they also claimed the day before invading Ukraine they had no plans to do so. These are just bald-faced lies, and I think it's important to differentiate between that and "it's not possible to tell what the real truth is" scenarios.
North Korea claimed to have found a unicorn lair (https://www.theguardian.com/world/2012/nov/30/unicorn-lair-d...), but the existence of unicorns is not in dispute.
Russia claimed to have no involvement in Crimea (later admitting they had); they also claimed the day before invading Ukraine they had no plans to do so. These are just bald-faced lies, and I think it's important to differentiate between that and "it's not possible to tell what the real truth is" scenarios.