[Baertram]

Just to make sure I understand you correctly:
Your 3rd screen is supposed to show the off-hand dagger equipped as well to see the additional weapon damage done?
But you only got the main hand equipped on that screenshot.
The off-hand slot (shield icon) is empty, there is no 2nd dagger equipped.

You'd have to equip both to see the actual values I believe.

And the green arrows should show you the difference of the main-hand equipped to the item you have moved the mouse over in your inventory at the time the screenshot was takne (I assume this was the off-hand 2nd dagger).
So it compares the values of the 2 daggers, which should be all the same, if they are identical. But maybe the tooltip recognized the same set items and calculated a 2 item set bonus of hundings rage then, increasing your values of crit by 657 ?