Table S2301 (Employment Status) - population universe question

Hello,

While reviewing table S2301, I noticed that the population universe seemed to change in year 2018 for population sub-groups.    Specifically, I am looking at 1-year ACS numbers for Disability Status -> with any disability.

If I am reading the table correctly, it looks like between years 2015-17, the population universe was age 16+.    But starting in year 2018, the population universe changed to age 20-64 years old.

Am I reading this table correctly?   If so, does anyone have more insight into why the table change?    I could not find any documentation.   Thank you -

Brian Parthum