Since the gland nut is threaded, the thickness of the washers does not matter. They are only there to sandwich the rubberized cork seal between them and squeeze it down onto the tube. The idea is to make the seal tight enough to prevent leaks without restricting the sliding movement of the tube as the rear springs flex.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!