As far as Gungnir (80) goes, the picture that was originally there was named File:Gun4.jpg, created almost nine years ago. Convention asks that images be named after the item they describe without abbreviation and 'Gun4.jpg' was deemed too ambiguous. I capped the replacement myself and saved it as , PNG as I find that format easier to work with, and replaced all instances of File:Gun4.jpg with the new image, then removed Gun4.jpg once it was no longer used on any pages. Unfortunately wiki does not make it possible to preserve the file history of a .jpeg replaced by a .png as there is no way to modify the reported MIME type of an uploaded image page. The only replacement strategy that works is what I have just described.
I apologize if this makes your efforts feel futile. Understand that my goals here are to update as many item pages as possible so that they can be reliably included in modern templates being developed that make the site more mobile-friendly as well as use modern features on the desktop browser version of the site. This often includes replacing images to meet this wiki's media naming and image policies, both decisions intended to make it easier for active wiki editors to make more changes down the road.