Because they are slightly ` tweaking` the standard specifications which apply to a stock-system, in terms of the amount of grey hair you require...... stocks are turned-out from the factory with standard density, wave and base material/size, and John has a certain number on hand at any given time.... they produce stocks daily, so if a person wants a little more grey added in, John simply mails them and asks for that percentage to be added in/on to one stock system in the batch, hence the slight delay in that he wouldn`t have it to hand to ship out immediately....it has to come from the factory.