Does Tiffany issue a valuation for their DBTY pendants?

I would absolutely add that. I have my plain platinum band on my policy. It might be easily replaced but it would leave a dent on my visa statement for sure.

If you have no other paperwork, I would submit the receipt to your insurance company. If they're anything like mine, every 6-12 months there will be a valuation increase done by them automatically to handle to rising value of metals and diamonds.