Just to get my $.02 in, Susan of DT, we've had similar experiences. John and Tony were the first English harmony singers I ever heard, and their recording "Spencer the Rover" is the reason I came to love that type of music. So when you hear me attempting to sing like that, it's their fault!

Frankly, I've heard a lot of performers frequently change the words to their own songs. Yes, a specific song may have been recorded and/or written down and copyrighted, but the darned things don't hold still if they're out of the glass case.