My thought process, if someone handed me this code and asked me to fix it, would be that they probably didn’t expect df[‘index_value’] to hold df.index

Just because, well, how’d the code get into this state? ‘index_value’ must have been a column that held something, having it just be equal to df.index seems unlikely because as you mention that’s always been available. I should probably check the change history to figure out when ‘index_value’ was removed. Or ask the person about what that column meant, but we can’t do that if we want to obey the prompt.