Lighter writes: "It's hard to believe that anyone could alter a song 'almost out of recognition' quite 'involuntarily'"

I'm not so sure. I've learned songs from singers, sang them in various places over a couple of years and then, going back to the singaround where I first heard them, heard the "original" version again and been shocked at just how much I've deviated.

Of course, there have been occasions where I've made quite deliberate changes to words and tune and then it's fully voluntary and I'm quite conscious of what I'm doing. That's something different. But over the course of just 2/3 years, I can testify to the fact that it's possible to deviate a lot involuntarily if you're not returning to a recorded version or written-out tune that's keeping you close to the original.

I acknowledge that such "drifts" may just be a product of my peculiarly wandering mind, but I still think it's worth noting that what Lloyd says here is not all that unbelievable.