I've proven that to mysefl for months now. Using the prep described in the 1906 booklet that I got the cold water shave out of. Lather on your dry face, rub the lather in vigorously, re-lather and shave. I've done this for what seems like forever now and the shaves are as good as when I used to wash my face twice vigorously, with hot water, in the shower. No difference.
On to the Derby blades ....... I hated them. I wrote rants against them on another shaving forum before I came to SRP. I could not fathom other people liking them. So I stuck with my Gillette Swedes and Feathers. Merkur and Wilkinson were also good as well as the red Israeli Personnas. Months later I returned to the Derby blades. I found them to be gentle and forgiving but effective.
I re-posted to that effect. I was getting good shaves out of them. To the point where I bought a large quantity of them on ebay. So what was the difference ? I think it was my technique. I had gotten better at shaving, manipulating the razor. There is no question that one man's favorite blade may be another man's worst, but sometimes returning to a blade that appeared to be useless 6 months ago may offer a surprise. YMMV. :)