For example the Japanese thought they had destroyed the USS Enterprise several times. Were any of the factions in WWII notably successful at hiding losses or convincing their opponents that active units were missing?
The Enterprise was reported sunk by the Japanese more than any other ship in the American fleet, (Source?) but this was not because the American high command was actively trying to cause the Japanese to think that. It was because the Japanese pilots and submariners, the only people to set eyes on an American carrier reported and beloved they had sunk her.
Another instance which this occurred was durring the battle of Leyte gulf. The Japanese attacked the Taffey 3 task force with everything they had, and the reports of the engagements with the Americans went along the lines of, 11:30 Baltimore class cruiser observed expoding and sinking. 12:00 destroyer torpedo attack sinks 5 fleet carriers, 2 battleships, 3 cruisers, and a hit on a light carrier. Even though Taffey three consisted of 5 escort carriers, 3 destroyers and a few destroyer escorts.
These inflated casualty reports weren't intentional misinformation, they were simply the best guesses durring the fog of war.
Sorry for the lack of sources if someone could back this up I would appreciate it.