Sure, Jennifer Garner looked lovely in Valentino at the Oscars, but what about the frocks that never made it to the red carpet? ''Three [other couture] dresses were custom-made for her, but they just didn't work,'' says her stylist, Rachel Zoe Rosenzweig. Great for Valentino, not so great for those other designerswhose fortunes can hinge on a red-carpet hit. Other Oscar switcheroos included Kelly Lynch wearing Zac Posen despite an Armani press release that boasted she'd chosen its ''charcoal/black dress'' and Angelina Jolie forgoing Chopard baubles for a $10 million H. Stern necklace. ''If you want to be in the gameand it's not for the weak of heart you just go with it,'' says Susan Ashbrook of L.A.-based Film Fashion, which reps Chopard. ''[Angelina] didn't end up choosing Chopard, but...she'll consider it for other eventsand there are always other events.''