Answer
For an IAL-based data source (and likely the same for some custom views), a missing column in the selector dropdown doesn't necessarily mean it can't be used — you can type the column name directly into the relevant field manually instead of picking it from the dropdown list, and the data source will still work correctly with that manually-entered column even though it wasn't offered as a selectable option. It's also worth refreshing the Dictionary Cache first, since a newly created or modified view sometimes needs that before its columns are picked up at all, though this alone doesn't always resolve the column-selector visibility issue.