I teach art and sometimes use a DVD and the accompanying book as part of my lesson. Almost every time I do this I find the book and the DVD don't "match". For instance none of the paintings demonstrated in the Geoff Kersey DVD "Perspective, Depth and Distance were actually in the accompanying book of the same title. I have recently been using Geoff Kersey's DVD of a demonstration of a painting of London Bridge and, although, at first glance the painting on the DVD and the one in the accompanying book on London look identical they are not. The colours and techniques are different. On the DVD he uses certain brushes and colours and in the book the materials are totally different and many parts are painted in a different way.
It's not Geoff who is the only culprit in this - it is the same with almost every book and DVD set I I have used. Wendy Jelbert's on Doors and Windows was particularly bad that way. Now it doesn't matter to me too much because I am a professional artist and only use these DVDs etc. to show my students some different examples, but if I was trying to teach myself watercolour and buying a book and DVD to work through I would find it very confusing. Why does this happen?