Here is an internal Harper's Bazaar document that lists the brands to feature in upcoming editorial spreads, ranked according to priority — and helpfully divided between "Advertisers" and "Non-Advertisers." This is how your ladymag sausage gets made.
A careless staffer left this brand list (click to enlarge), along with call sheets for three shoots, on the desktop of an L.A. hotel's public computer, where a Racked tipster found it. It's not exactly a shocker that ladymags are in thrall of their advertisers — remember the Marie Claire "editorial" that was comprised only of clothes from Ralph Lauren, Ralph Lauren, and Ralph Lauren? — but it is rare that concrete proof of these relationships emerges.