I think you refer to a factoid, Robitty. Doesn't make the wrong information a fact though ... it remains exactly what it always was and that is misinformation.
Madeleine's case has suffered immeasurably from factoids in my opinion; not one of which has assisted her recovery in any way whatsoever.
"factoid
noun
an item of unreliable information that is reported and repeated so often that it becomes accepted as fact." First problem is that definition is different than what I thought factoid meant. I see I'm not the only one "Due to the confusion surrounding this word, I can absolutely see where they are coming from as “Factoid” has two somewhat distinct definitions, one being more or less a subset of “Fact”, the other not meaning the same thing at all as “Fact”.
http://www.todayifoundout.com/index.php/2010/02/the-difference-between-a-fact-and-a-factoid/So if it is a factoid then what is the unreliable bit of information? The claim that Martin Smith saw Gerry is definitely an unreliable bit of information for it is more than what he said in his statement. But that is not the reason I would say the Smith sighting is a hash, Fact. Well it could be that I interpret the word hash differently! What does "hash" mean to the rest of you?
What does the phrase "the hash of the Smith sighting" mean to you?
"hash
noun
1.
a dish of cooked meat cut into small pieces and cooked again, usually with potatoes.
verb
1.
make (meat or other food) into a hash.
2.
come to agreement on something after lengthy and vigorous discussion.
"they met during the day to hash out the campaign's reaction to the controversy""
Well I have a different meaning again like hash means something like balls-up (is that a word?). Balls-up is more like the cooking use of the word but applied to an outcome. The result of a total mix up.
"balls-up
noun BRITISH vulgar slang
a bungled or badly carried out task or action; a mess."
Another Urban dictionary gives the reason we call it a balls up "The term dates from the days of wooden sailing ships when the existence of a shipboard disaster, such as plague, lack of food or water, mutiny, etc. was communicated to the outside world by hoisting large-ish, brightly painted wooden balls up into the rigging. Balls of different colours represented different disasters ...."
You live and learn.