He definitely counts GWP sales returns as part of the discounts he says he can get on sets. He has said so specifically when talking about how to get discounts on things like modulars. His claims of getting those discounts are counting money from sold GWPs, credit card cashback, VIP points, and all other forms of potential cashback(Honey, etc.) stacked together.
Though that Stranger Things BH set being Lego exclusive means you can't buy them in bulk(limit 2 on SAH), and being that they are $20 ea. $40 is hardly netting you a particularly great GWP.
I mean if you could buy unlimited amounts and you bought say 8 of them for $160 and that qualified you for a good reselling GWP like Forestmen's Hideout($150 buy-in) that you sold for $40 after shipping and fees. That would be a 25% discount that you had to work for, then 5% VIP discount, maybe 3% from a good credit card cashback program. Still that's only in a world where you could actually buy in bulk which isn't real, which means you have to be buying other sets from SAH to hit a good GWP threshold, and anytime you are purchasing from SAH you have opportunity cost with regard to savings unless they are exclusives.