When one get the "sold listings" only the total price for the home is given. It is not broken down for lot value and house value. The tax assessor, on the other hand, comes up with a value for the house and a guesstimate for the lot.

When doing an appraisal, the specific adjustments that effect the lot (slope, location, noise levels, view … etc.) should be taken against the lot. Most of the adjustment are usually made against the house. For practical purposes, most developed areas have few recent sold vacant lot data points to obtain a large enough sample for estimating a lots value. So when estimating property (house and lot) value for a tax appeal, one makes adjustments against the figures the assessor assigns.

In real life when doing an appraisal, one does not come up with a figure for the property and then the house. It is not broken down that way. When one does an appraisal for a vacant lot, then one has to obtain recent sold data points from recently sold lots to make an educated comparable analysis.
Again, those data points are complicated when a home is place on the property since many factors and influences go into WHY the home sold for what it did. Only the magician tax assessor seems to be able to pull figures and assign lot values out of their hats.

As a matter of practicality, we don't come up with lot's value, the tax assessor does. Our only data point is only a sold price for a house. We have to figure out in the end how to distribute the final adjustment value for the house and assign a portion of it to lot value or house value. When we win the case the tax assessor may juxtapose and assign a different value to lot and house.

The important element is the quality of recently sold comparables that are closest to the subject property in location, time of sale, and square footage.