Dawkin's explanation of a stub combined with Attenborough's comment about the flying squirrel's wings being a "very valuable asset" should give you your answer.

Evolution is essentially a generations game. Any accidental mutation of a stump that turns out to be a biological advantage will be passed on to the next generation, and so on and so forth. Virtually any "stump" could evolve into a wing given the proper habitat and the creature's need for a flying ability to survive.

Eons of time helps, too.

Could you give a hypothetical example of what you would consider to be a 'fact'?

From my point of view, it can't get much more factual than this sort of example. We're looking for changes that occurred to a species over millions of years, and any one particular creature or fossil is only going to represent the tiniest snapshot of that species' evolution in time. It's simply not possible to find a fossil that will encompass the entire transition of no-wing, to wing, all at once. The fact that we have evidence of animals between these two states should dismiss any theory of "There is no possible way a wing could have evolved", which I believe was the point Dawkins was addressing.

That's Dawkins's most famous homologous structure, or vestigial (maybe) organ. It proves that Dawkins evolved from small ape-like creatures that foraged in the tropical meadows of the Jurassic Period. The fact that your eyes hurt goes to say that perhaps the shirt organ has a function still: scaring away BoogeBoogiestons, which are burrowing creatures often found in meadows also. Dawkins likes firm ground under his feet.