What does 0 represent in degfield variable of education-person group? Its not listed in codes but is included data

I extracted field of degree variable data under education-person group from IPUMS USA between years 2010-2015. There was a variable label “0” that has a count of over 6 million. What does the 0 represent? I see that the code “11” represents the label “agriculture”, but the code “0” also has a label “0” when I ran a tab command in stata. (The tab command in Stata lists the variable’s labels, frequency or count, etc.)

A value of zero in DEGFIELD represents “NA” indicating that the respondent didn’t report a field of study. This can be seen more clearly if you look at the detailed codes under the codes tab. This detail has been fixed, so that the value for “NA” shows up for the general codes as well, and will be updated with the next data release.

Thank you. I see that the frequency associated with 0 equals the cumulative frequency of those with less than a bachelor’s degree. Since my data set included from education levels from high school to bachelor’s degree, those are the observations coded 0.