I completely agree with DrZZ's comments: you MUST not use CAS numbers as your primary database key! This will work, well, until the moment that it doesn't work any more... which is the moment that you most need the system! As for the problems of curating CAS numbers, you should take a practical stance: do you use CAS databases to find the boiling point of acetone? Of course you don't! Neither are CAS databases used to find the CAS numbers of most commercially available compounds. I can only hope that CAS's stupidity and greed will not affect the normal progression of science.