Some of this writing could be very desirable. I have some 1000 word articles in fertile niches that I think would yield a good payout on constant-content or other content brokering sites.
If you sold content to a client at least a year in the past and the content was never used, would you feel it would be unethical to re-sell it?
If I'm using a free website that scans for plagiarism and I'm not finding any existence of the content on the web, could I potentially be missing things CC would catch? I last thing I would want to do is get accused of plagiarism on CC.