It's interesting that many of these businesses are basically real estate holding companies. I wonder how many of these businesses are just tax-minimization or financing schemes used by larger companies for things like deferred compensation?
a) modest real estate holdings: a block of apartment buildings and a couple commercial properties.
b) a large, successful construction company.
c) operator of roughly a dozen franchise locations.
d) is anyone's guess; outlier software firms, well-compensated financiers, CEO maybe.
I know this doesn't address your question. Modest landholding is a common way to be in the 99.5.