Ownership can cross subdivision lines. That isn't common, but it happens. With the advent of zoning restrictions it became legally "impossible" to split existing tracts with simple deed grants. Although violating the subdivision regulations between two parcels with developed lots doesn't really come with any penalties. It's when a building permit for a house, addition, fence, driveway, ect is applied for. Then the hammer comes down.?ÿ
Almost all the partial lots (there are many of them) happened before 1975-the date of the zoning act.?ÿ
In a county where I used to live in Colorado far far away from reality the assessor's office used to routinely perform combinations splits replats boundary line adjustments and whatever the hell else they wanted to.
It made for some very interesting mapping for sure because the original lot lines are always held and the new lot lines would be on the highest layer in the GIS.
Whenever I asked why do we do it this way they always looked at me and said well you should know you used to work in land surveying.
I'm back in land surveying and not doing GIS anymore. Thank God.