Not sure if this is where I should post this or not.

I have been looking at the Photoshop for Digital Photographers DVDs by Colin and here is the question. I have been wondering which one to get. I have a couple different versions of PS now and I wanted to know are there different tricks on each version? Or does he go over stuff he has already gone over in the previous versions just updated with the newest versions of photoshop? Cause if he teaches a bunch of tricks that are different per DVD I am wondering if I shouldn't just buy the newest one and then some of the older versions of the title as well...