Source: https://fred.stlouisfed.org/series/LNU01074597
Okay, So, ignoring how shit all that is. 
I finally found info on how these numbers are acquired.
The Current Population Survey (CPS) is a monthly survey of households conducted by the Bureau of Census for the Bureau of Labor Statistics. It provides a comprehensive body of data on the labor force, employment, unemployment, persons not in the labor force, hours of work, earnings, and other demographic and labor force characteristics.
Here's what I feel are the 2 most important points from the FAQ on disability data
How are people with disabilities identified in the CPS?
The CPS uses a set of six questions to identify persons with disabilities. A response of “yes” to any one of the questions indicates that the person in question has a disability. >The disability questions appear in the CPS in the following format:
This month we want to learn about people who have physical, mental, or emotional conditions that cause serious difficulty with their daily activities. Please answer for household members who are 15 years old or over.
Is anyone deaf or does anyone have serious difficulty hearing?
Is anyone blind or does anyone have serious difficulty seeing even when wearing glasses?
Because of a physical, mental, or emotional condition, does anyone have serious difficulty concentrating, remembering, or making decisions?
Does anyone have serious difficulty walking or climbing stairs?
Does anyone have difficulty dressing or bathing?
Because of a physical, mental, or emotional condition, does anyone have difficulty doing errands alone such as visiting a doctor’s office or shopping?
Labor force measures from the CPS are tabulated for persons age 16 and older.
Are the questions asked about everyone in each household every month?
No. The CPS questions for identifying individuals with disabilities are only asked of household members who are age 15 and older. (Labor force measures from the CPS are tabulated for persons age 16 and older.) Each of the questions ask the respondent whether anyone in the household has the condition described, and if the respondent replies “yes,” they are then asked to identify everyone in the household who has the condition. The CPS is administered to a household for 4 months in a row, followed by 8 months in which the household is not part of the survey, and then the household is again included in the survey for another 4 months. Those households that are in the survey for the first time, or for the first time after the 8-month break, are asked the disability questions. Replacement households and new household members are also asked the disability questions. During months that the questions are not asked, the responses collected earlier are retained to establish disability status in the same manner used for other demographic questions (about race, sex, etc.).
HMMM!
Because of a physical, mental, or emotional condition, does anyone have serious difficulty concentrating, remembering, or making decisions?
The brightside is that I know there were quite a few of us that were worried about that dip in 2020 being from the deaths of people, but I don't think that's the case. If you look at the graph in a less compact form, the dip starts in March (far before deaths peak) and is spread out over the entire course of 2020. Based on how often the questions are asked I don't think the data itself would show deaths that visibly. Plus, looking at the questions, I actually kinda think that dip may be from people having a bit of breathing room thanks to time off from work and all the "assistance", relatively speaking.
