How to count the number of completed portions of a roster

I have a roster ( RPOPULATION ) that is based on a list question ( names ) listing the members in a household. The list question names is also used in another roster hhroster that asks for some basic information such as age and sex. I have an enabling condition on RPOPULATION that chooses only selected names from names based on variables in hhroster.

I would like to have a variable that counts the number of completed “questionnaires” of children in RPOPULATION . I’ve seen the section functions (https://support.mysurvey.solutions/syntax-guide/functions/section-functions/) but I’m not sure how to get them to work with a roster. For example, in the image below, I would like a function that indicates that of the three children questionnaires, that one is completed.
image

These functions are applicable to sections, not rosters.

If you need to make sure that all of the questions about person-i are answered, make sure there is a sub-section (SubSect) containing all the questions about that person in the roster (PersonsRoster):

IsSectionAnswered(PersonsRoster[i].SubSect)