The partial exclusion exists for people who do not meed the 24 month requirement.  It is just that in your case 1) it doesn't seem like he meets the requirements for a partial exclusion and 2) even if he did the exclusion would be zero, because in the 10 year period (extended due to military service) between Sept 2008 and Sept 2018, the taxpayer lived in the home for 0 months.