What to do with 6XX _4 subject headings on non-DLC/DLC records:

1. delete the 6XX _4 heading when there is a legitimate 6XX _0 heading which is just like the 6XX _4.
   
2. when there is not a matching legitimate 6XX _0, check to see if the subject heading in the 6XX _4 field is in fact a legit LC subject heading. If it is, change it to 6XX _0. If it is not legit, delete it.