I always say 'a good lily is where you find it'. Sometimes a person can make some really nice heirloom discoveries in those old well maintained gardens. That makes this lily kind of unique and worthy of some further propagation. A good lily grower who's been around a long time might be able to identify it quickly. Send a picture to B&D or The Lily Nook and see what they say.
Edit added: OOPS-- Add 'The Lily Garden' (Judith Freeman).
