We only know four things for sure:
a) 450,000 Dash were stolen from Cryptsy
b) All those 450,000 Dash were sold over the last year
c) All those Dash are now gone; the dumper has exhausted his coins
d) 450,000 coins dumped on the market over the course of a year would have a significant impact on the price

Where is the proof the 450k stolen Dash have been "sold off already?"