Not including Mathmos, what are the general guidelines to determine the age of lamps outside of dates on the felt? And how to match up 'original' bases and globes? I've seen UL stickers that are white with blue letters/trim, blue with black/navy letters/trim, white with brown letters/trim, white cords, black cords, brown cords. Bases with white plastic plugs to fill the electrical cord holes that light up, black that don't etc. etc. I've studied hippielight.com & endoftherainbow.com as well which has been quite helpful. Any other suggestions? THANKS!