Hi, when I originally created the valuation guidelines (after a couple rounds of feedback before and after), incompleteness (which this is a subclassification of) was given a flat 50%.
>>The total weighted condition for all of the elements is calculated. (Weighted condition is looked at instead of base condition, to allow for adjustments for incompleteness and shrinkwrap, since the Acaeum doctrine is currently that shrinkwrap will be a qualifier only, not a condition level, and that incompleteness degrades value.)
>>Weighted conditions are as follows:
• For an incomplete item, the weighted condition equals the actual condition x 0.5.
There was discussion on fine-tuning this a few times during my tenure, but I can't find the conversations right now. Basically, incompleteness is regarded as a qualifier (percentage modifier) to condition, since it's (a) impossible to tell from a scan if an item is incomplete and (b) a field replete with uninformed sellers who might say an item is complete, sincerely, even though they're wrong.
Condition curving was discussed, but it got too complicated trying to factor in levels of completeness. (Is it 90% complete? 75%? 63.2%? What if one counter is missing and everything else is pristine?) The .5 modifier averages out well over numerous auctions. Also, there are not enough data points (auctions) for incomplete items to arrive at an accurate valuation without handling every item to determine incompleteness, which is impossible.
On a case-by-case basis, I simply recommend treating incomplete items as non-collectable. I simply treat such items as resellable, not collectable, and what you get is what you get. But admittedly I'm a completist when it comes to true collections and my viewpoint might be considered toward the extreme end.
You can see some interesting bits of "items missing" grading on a quasi-related field over here:
http://gotcha.classicgaming.gamespy.com/conditions.htm
