Flapping propellers
To account for an eyewitness describing the Wrights' propellers as "flapping" I don't think we need to postulate a change in meaning of the word (which seems a bit unlikely to me). We just have to remember that eyewitnesses are extremely unreliable, and the slow rotation of the Wrights' propellers could easily have been interpreted, by a relatively distant observer who didn't know how they really moved, as flapping. Think of all the times you've seen something as first moving in one way, then identified it and reinterpreted it.
Truly, eyewitnesses are unreliable. All those aircraft that streak flames before crashing, even though there was actually no fire. And it's not just other people: I was an eyewitness to a mild fender-bender, and afterwards realised I could not remember the precise sequence of events.
I'm not quite sure what OP is trying to prove. I assume it's that someone else had priority over the Wrights, and it looks like Langley: maybe Langley could have flown, but he didn't. But if the Wrights didn't really fly until 1908, that would give it to Santos Dumont, unless it was really Richard Pearse: but if Pearse was first, it shows how little this Guinness Book of Records mentality matters for real history, because he had no influence on future developments, whereas the Wrights, for good and ill, certainly did.