I'm also old enough to remember a lot of Churchill. I'd be glad to bet -- loser makes a donation to Free Republic (and winner, too :-) ). And I'd be delighted if I guessed wrong and all of these quotes are authentic. But I don't think we could ever settle the bet.
Churchill, like Lincoln, was so quotable on his own, he's picked up lots of apocryphal quotes over the years. In time those show up in supposedly serious sources. I suppose that's normal -- people say, "Wow, that's a great sentiment, I'll bet Churchill said that," and attribute it to him without looking it up. The next thing you know, it's in a quotations dic. 200 years from now, some scholar will sort it all out and say, "I can't find anything in his writing that he said this, this or that."
Most are attributable to Churchill for two reasons. One, he was a much feared and despised person in government and power circles. They were only too eager to subscribe anything to him they could. The other is that Churchill spoke out on very controversial subjects, thus most willing to give him his due.