Would Somebody Please Explain

The comp used for this property sold fairly recently, on 3/2/18.  It sold for $641k.  After comparing the property details of the comparable property to the property details of the target property, the County Assessor’s office adjusted the sale price of the comparable property down $20k, to $621k. 

https://revenue.stlouisco.com/IAS/

Except that the comparable property IS THE SAME AS the target property.   The property that recently sold was used as one of its own comps. 

I don’t understand this adjustment.

I could understand if they had increased the sale price, because the housing market is improving, and a house that sold nine months ago should have increased in value, even if just minimally.  And I could understand an increase if the new property owners had done some improvements since moving in.

But being as it’s exactly the same house, why in the world would the sale value be adjusted down?

Per the County …

https://revenue.stlouisco.com/IAS/

….except that in the example above, THERE ARE NO DIFFERENCES.  The comparable and subject properties are the same property.

And then, after determining that the real market value of the house was not $641k as it sold for, but was actually only valued at $621k, they then calculated the “Market Value Estimate” to be $755k.

  

This example is not at all unusual for recently sold properties.

By the way, is the actual Statistical Model Estimate for this property $753k or $741k?