Chopper, you seem determined to conflate two different things.
A Quick Throw-in may be taken under certain rigidly defined circumstances. Amomg these, specifically it cannot be taken if 2+2 are present at the place for the Line-out. If those 2+2 are present then what is being attempted, cannot - by defintion - be a Quick Throw, and must be a Line-Out; and the ref will then simply apply the Laws relating to Line-out.
Conversly, if 2+2 is not in place then what is being attempted can only be a Quick Throw, and the ref will apply the relevant laws, and if all met, play goes on.
There simply cannot be a situation where there is doubt. If a Line-out is formed (2+2) then the QT is impossible, if it has not formed then the Line-out is impossible.
The only possible doubt is in the refs mind - has a linout formed, is it the same ball, etc. ... in that case he simply makes a judgement and what he says becomes fact, and the game moves on from there as described above. (and following a discussion later with an assesor so may the referee)
It's either a duck, OR it's a pig with lipstick - the two are mutually exclusive.