It is weathering, what is the difference?
Spots will start to rust at different times, thus rust will appear more or less progressed in different places on a given piece. This is also true of dribblings and dirt. Paint will also fade unevenly.
Depending on the size of the area that the glue got, you could also put a dent, damage or a patch. If the piece sat under a tree or under roof eaves for some time, it would have the results of repeated pigeon dive-bombing practice over a large area.
