Fons, I've been around the free-software block a time or two and I have to say I have never *once* encountered the latter form of notation. Adding a Copyright (c) line with dates is the standard practice, but (obviously?) only to files that have actually been altered significantly. Anyone interested (even those weasely lawyers) can run a diff against the two codebases to see what was actually changed.
 

Who cares? Yes, that's the first thing a young, naive developer is going to do. Fork some big project with grand intentions, go ahead and smear his filty moniker all over the source, and then.... nothing. Nobody would have ever even known about this fork if you hadn't brought it up. It would only become relevant if it actually offered something you don't. And on what grounds would you prevent that? Because making something better is somehow perverting it? That's life. No ill will here, Fons, but I hope you don't think you'll live forever. One day you'll be gone and somebody will get their filthy mits on your code. That's better than having it die with you, don't you think?