Call me cynical if you like, but when it comes to nutritional suppliments such as glucosamine I think you will find that 99% of those telling you that something is good for you are trying to make money out of you.
If your own personal research is a trial of one individual then it is impossible to rule out the placebo effect, as Detritus says, also you can't rule out that the pain might have gone away on its own without treatment.