Units in Structure

I am preparing a report for Arapahoe County using 2015 and 2010 ACS data. In the "units in structure" table for census tracts, I noted a large number of negative numbers for total housing unit change from 2010 to 2015. Census staff found an error note in the 2015 FactFinder display that described problems with the vacant unit information for 2008 to 2015 ACS. That explains part of the problem but I have 18 tracts with a loss of more than 100 units. That seems like a lot for just missing the vacant units.

I wonder if there was also an adjustment after the 2010 Census results were known that might have dealt with tracts where the pre-census estimates were too high.

Any thoughts