Don't put too much stock into those 7 year half life formulas.
When EMs gave way to SS, operators found that even a 1 year old EM looked and earned like a dinosaur.
Often, you could not sell an EM for even $50, and some ops had a rule 'never sell a used game to the public, or they will stop playing on route" - so many games went to the dump.
When SS games gave way to DMD games, you could still get a hundred or more bucks for them. Professional auction companies like American Amusements would even advertise and (gasp!) sell directly to the public.
So rather than going to the dump, many SS games went to the relative safety of people's Rec Rooms.
Looking at that chart in 2008, supposedly 75 Quicksilvers were in people's homes.
Now in 2015, are we to believe that 37 of those games have been destroyed? How?
Of course very rarely we hear of a fire or flood, but not 37 of them.
I personally know where 11 Quicksilvers are, so there is no way that I magically have a line on 1/4 of the remaining stock.
There are many hundreds still out there.