Don’t Use Merge and Center
If you’ve got a table and it’s missing some data you will be tempted to put in a N/A and merge all the cells so that N/A applies across all columns/rows. But that makes it impossible to sort the data—you can’t have a merged cell in the middle of a sortable table.
Instead, select those same cells, right click and go to Format Cells > Alignment, and under Horizontal Alignment pick Center Across Selection. Now all the cells appear merged, but they’re not, so you can still sort.