Aha! the puzzle is finished! And believe it or not—-all the pieces are there!
I can’t believe it!
To finish the puzzle I had to bring up my most draconian method, my most rigorous method! I have seen my granddaughter and son-in-law use this method, too–I guess when the pieces just look too much alike to make much headway.
In a nutshell, all the unused pieces must be arranged by type—4 knobs all around, or 4 holes all around, or knob at one end and 3 holes, or slanty wiggily end on one side, or nondescript. These are put into ranks and files (and lines) and then when it looks like you might have the slightest clue of a missing piece—hopefully at least 3 sides of it, then you can go to that column to hunt for the piece.
That’s the way I finally broke through on the Blue Moon puzzle. Big sigh of relief when last piece settled in with a “thunk”.