I finished the puzzle with three missing pieces and one extra. Moving the furniture around revealed a piece.
When I mentioned about 2000 pieces ago that there was a piece missing, people wondered how I could be so sure at that point. Well, because I knew I had run out of blue pieces. I wasn’t sure about the rest until last week.
I’ve read online that it’s possible to ask the puzzle’s manufacturer for missing pieces, so that’s my plan. One has to count the lines and columns from a point of reference (e.g. from top to bottom and left to right). I wonder if I should send back the extra piece. Presumably there is a puzzle out there missing it.