When printing a new negative, I do it all the time.
I cut a 3.75x8 piece off of a sheet of 8x10 paper (which is used for test strips) then I make a 5.25x6.75 print on the 6.25x8 piece left over, which gives the maquette a bit of a white border.
I can work through a whole bunch of these before moving up to larger print sizes, because exploring a negatives potential and basic dodging, burning and/or masking needs is way cheaper at 5x7 than it is at 11x14 or 16x20. I let these dry over night, flatten them, and live with them for a while before going up in size. Things always change when I do go bigger, but it sure gets me close.
Using paper from different emulsion batches isn't a problem, because where I live it's cheaper to order 50 sheets of 16x20 than it is to buy 200 sheets of 8x10, so I just buy 16x20 and cut it down to whatever size I need.
Being less than affluent (HUGE understatement!) I started doing this when I began to feel I was making final prints before I should have, based not on what the print needed but by how much money I was throwing away into the darkroom garbage can.
I don't have the book you mention, so I don't know what Edward did...can you fill me in?
Murray