Jigsaw Puzzle...

Here's my current jigsaw puzzle... It's another second hand puzzle and the lady said it was complete... It's been a good one to work on... Just struggling with the cloudy sky... I'm still missing 1 piece from the bottom right hand side...
My question for those that do jigsaw puzzles - do you mark the box saying it has a piece missing, do you not worry or do you just throw the jigsaw out ???