Apparently at some point in the past three pieces were removed from the sides of the painting.
> That’s why we’ve had so-called artificial neural networks working overtime on reconstructing the original appearance of the painting. Hour upon hour, the computers have been whirring away, recreating these missing pieces on the basis of a 17th-century copy.
Interactive comparison of the missing pieces:
https://www.rijksmuseum.nl/en/stories/operation-night-watch/...
Zoomable image with the missing pieces added back in:
replies(1):