Look at photos of surviving pieces in museums, learn to distinguish bobbin from needle laces. Looking very closely at the photos you will be able to see how the threads run many threads woven together is characteristic of bobbin lace, solid areas appear to be woven. Needle lace is made with only one thread looped over itself in variations of the buttonhole stitch.
Solid areas appear to be knit.
Learn to make the stuff - you will soon find yourself able to recognize period lace from across a crowded room. Choose threads that look like natural fibers or real metal. Sometimes 2 or more colers were used. Cotton is just fine, but should be starched. Ask for Cluny, Le Puy, or Torchon style laces if anyone in the shop knows what they are.