Fill missing cells without hiding the rule
A fill operation is a data decision. Write down the rule that makes the replacement valid for this column.
Use a fixed value only when it has a defined meaning
A literal such as unknown may be a category in one dataset and a misleading substitute in another. Confirm that the receiving system distinguishes it from a real value before filling.
Use previous-value filling for ordered groups
Fill down repeats the last nonblank value separately for each selected column. This suits a report where a group label is intentionally shown only on its first row. It does not infer group boundaries or sort rows for you.
Review leading and whitespace-only cells
Spaces and tabs alone count as blank. In previous-value mode, leading blanks stay blank until the first nonblank value appears. Confirm that this behavior matches the source layout and keep the original input for comparison.
Try this workflow: Fill blanks. It loads a labelled fictional example that you can edit.