Well, discounts do start early when you buy multiple model packs at the same time, and they rise in 5% steps, but there is a ceiling (or floor, depending on which way you look at it).
If you are aiming for more than that, write to tgc making an offer.
I wished I had foreseen that, in the course of time, I would buy almost all of the model packs, then I would have done as I'm telling you (but I started buying when only a few packs were available).
But do your homework, there are so many bundles available offering massive extra discounts that combining them in the right way could also be interesting enough to make calculations worth while.
Lives of great men all remind us we may make our lives sublime
