Don't sweat it. I've got to head off to work really soon also! We can verbally beat each other up tonight. ; )
I am though still curious to know what your answer is about how someone is supposed to know what is and what is not copyright protected.
Quick response..... one should assume that EVERYTHING is copyright-protected/patented/etc. Books, music, software, etc. etc. etc. EVERYTHING. Do a search on "intellectual property" and read all about it ;-).
I do my best to go into the local schools on their CAREER DAYS and educate the jr. high kids about the music publishing industry. I give them a handout with a FAQ about copyright. Education should start early, but I'm here to tell you as a personal example that one can get all the way through music school and not be educated - exc. "backhandedly" - about copyright and its implications and how to deal with it.