When does one unzip the window?

I normally leave mine zipped while lowering mine. but it's not the factory way to do it. yes it will scratch a new window. but on an older window that has hazed it makes no difference in that respect and may be hard to zip back up if it's brittle. I do wax my window zipper and have scotch guarded my cloth that the window is sewn to to help make it last a bit longer.
here is a shot of the 66 dart/coronet lowering procedure on page 77 in section 23 of the FSM.
View attachment !!!!!!lowering top pg 77 section 23.jpg