When I select multiple items and the blue title bar appears, there is an “update values” button on the bar. When I click on this button, nothing seems to happen. I’ve tried just selecting one item, and many many items. No matter how many I select, the “update values” button doesn’t seem to change anything.
Looking at your collection I’m seeing that for most of your books you have a “my value” filled in. This overwrites the value that can possibly come from Core.
I’ve just changed your view to LIST view and added the Value column. You can see the person icon indicating these books have a “my value” filled in: