I think it is the T2 Gems that is making the damage value show higher than the first two. Cause this gem has higher scaling.
The last one is not bound to you, so I think it is not calculating properly (I am guessing it is someone elses that you are viewing). What did you have equipped when you took the last screen shot?
I own all of them and they were all equipped at the time of screenshotting. 1st, 2nd, and 5th were all preview’s of the wep at 625 on the upgrade menus. I’ll have another look tomorrow but, I think the 5th one has more damage than the 3rd and 4th even at 624.
With the last one the green text is missing, so that is why I thought you didn’t own it. Was it maybe in the TP or inside a storage when you viewed it? Not sure what else could remove the green text, but I think that is what is messing the calculation.
Otherwise it is only the gem that should be making the difference. If you change the gem on the 1st and 2nd ones, do thier damage go up?