RE: Value on date of theft
Not really agree with you here. It seems reasonable to assume that stealing anything already in short supply will therefore push up the price. Even if the theft was not intended to inflate prices, and considering there are other factors to the price increases, the fact is still that the theft will have added to the rising costs.
As a real life, true, honest-to-God example you just need to look at Auric Goldfinger's plan to increase the worth of his own gold by effectively removing most of everyone else's gold from circulation (by making it nasty and radioactive).