Ebay completing listings would be ideal. Unfortunately, they only allow the past 2 weeks to be searchable. I found that there is, however, a 3rd party service that retains eBay sales data for the past year. It just costs a monthly subscription.
Terapeak is the one I've seen referenced often in eBay forums. (Note that I have never tried this service, so I can't speak to it. Just passing along some info.)
So it'd cost $50 to check the selling history of 87TDs during the past year. Might be worth it if we're talking a substantial $$$ difference in the outcome of your situation...?
Also, if any really nice 87TDs have been exchanged between forum members, perhaps they can provide you with a photocopy or scan of the bill of sale?