They both mean rusty/rusted, so is there any subtle difference between these synonyms or is one longer and that's it?
How you express the state of rust may vary from person to person, but I think that 錆びた and 錆びていた are obviously different.
Because it is difficult to explain with words, I searched for images by a keyword "錆" on the Internet.
Since I placed the representative images and arranged them according to my feeling, please have a look.
When something is very rusty, we sometimes say "錆｛さび｝さびだ！" to express it.