Development of Creative Commons licenses

[Jen Gagne <jen AT beware-of-art.com>]

Thanks for the reply, wiki_tomos. Oh dear... your explanation seems  
thorough, but somehow I'm still confused!

I mean, I think I have a basic understanding of how works derived from  
(for example) public domain photos can be copyrighted, in the sense  
that the remixing artist can copyright their newly-added original  
aspects and don't have to cite the original PD source (because it's  
PD)...

Does the "by" license mean that every future generation of work that  
includes an element from a previous generation of work requires an  
attribution back to whichever artist introduced that element originally?

If so, how is that different from the "by-sa" license?

As far as I can tell, in the text, the key difference between the "by"  
license and the "by-sa" license is section 4b. You also mention a  
difference in the Miscellaneous section 8, but as far as I can tell  
with Word's Document Compare tool, they're identical in both licenses.

My interpretation of section 8a and b, since they say "Licensor"  
rather than "You", is that it gives Client (in my example) the  
_option_ to use the original work with the CC-by license. But that  
doesn't mean the license carries on to the adapted work... does it?

So confused... @_@