Merge Queries returns blank

Can't solve this specific instance but here's how you progress.

Do a test to join only on one field at a time e.g Period. See if there are matches.  If not, then investigate.

Then try joining on another single field.  Do that for all three and see if any don't work.

If they work, then try a join on 2 fields, again see what works.  Ultimately you will find the column or columns that don't match - investigate that and edit the data to fix.