Indexes and other finding aids that are created to assist the researcher in locating someone are imperfect. Names are spelled wrong, transcribed incorrectly, accidentally omitted, etc. In most cases, it is possible to search the records manually to make certain the person is really not in the record.
Do not rely on an index to contain every person actually named in a record series with every name spelled correctly. Original records may have been partially indexed by the body who originally held the records or organized in such a way that may partially reduce the number of pages that have to be manually waded through.
I plan on researching the 1950 census manually when it goes online in April 2022. I’ll start with my rural people and then work on the ones in more heavily populated areas. Get ready for the 1950 census with my webinar–recording and handout included.