The formulas to calculate pricing of New aircraft and Used aircraft seem to be completely disconnected.
The same problem also happens in opposite direction. A brand new aircraft with list price of 100m leaves the production line, and the second it leaves the production line, it's price becomes $90m (as its recommended value). I noticed this in all of the popular lines in GW3: A320 and MD-90/B717 lines, NG.
This, while people place orders for the list price, and on top of paying the list price, they have to wait anywhere between 6 months to 3+ years to get the aircraft delivered (depending on line).
A brand new aircraft needs to be valued at least the List price of New aircraft.
And, as in your case, 5 year old aircraft needs to be valued at less than new aircraft, especially for a production line that is not full (as is the case with Saab 2000).
My hypothesis (of disconnect between New and Used pricing formulas) explains your scenario. I am assuming that the List price of Saab 2000 dropped below par, since there are not many orders in the production line. But the Used aircraft Value formula, is not aware of that, and prices Used aircraft as if the list price of new was still at par.