As a PO I want to see when a story was pulled out of order
A team member might want to pull just any story and there is good reason to allow this but it leads to confusion.
The PO might refrain from enforcing his priorities because might think it actually accidentally was the top story.
Also new team members seeing the possibility to pull just any story might not get the implicit-ish priority given by the product backlog sorting.
My suggestion is: Add an obstacle to the pulling of random stories by asking to provide a reason to pull this story and not the top one. This could create a comment on the story by the system user (is there a system user already?) reading "Tom pulled this story in out of priority. His reason was: We already implemented this story last year./Code was only commented out./Sorry, but I like this story better"
Idea is accepted and the Product Owner needs to create a Story of it.