(inspired by anachred's comment on previous "Kvetchin'" post)

Picture books are invaluable in researching historical periods for fiction. So are internet galleries. But! Just because an artwork is dated late 13th century doesn't mean the clothes are. We don't portray Jesus wearing surfer shorts and flipflops--so I can't assume that ye olde medieval people showed religious subjects in ye olde medieval clothes. Same with Arthurian subjects in the 15th century. In other words, a lot of art might have been deliberately SCA.

Then you have the big fashion changes that took place in the later part of the 15th century : the transition from medieval to "renaissance" clothes. If your characters are at the edge of that, you might have some with old-fashioned balzos--honking big bouffants, and others with more dainty, fresh coaz--with the hair bound close to the head with ribbons. Not yet for the long braids and jeweled hairnets of the second half of the quattrocento.