I make a three-bean salad with edamame, black beans, and chickpeas. My neighborhood supermarket stocks only the frozen edamame in the pod, so this is something I usually pick up without the pods at one of the bigger stores. The other night, however, I spotted the store brand, and it said "unshelled edamame." The photo on the bag was of a complete pod. I felt through the bag and it definitely felt like the beans were in the pod.
My mind was processing "unshelled" to mean there were no shells. So it looked mislabeled to me. I did a quick survey of friends, and most thought that "unshelled" meant "with shells" - that is, they had not been "shelled." It still scans as ambiguous to me in a way that "shucked," with corn, would not be. Merriam-Webster has a definition of the word "unshell" which means apparently the same thing as the verb form of "shell" - to remove the natural enclosing cover, as a shell, husk or pod. There doesn't seem to be a defined word "unshuck." Â
Wouldn't it be simpler to label them "in the pod"?
I am not sure how you propose to unshuck corn or unshell a legume. Â If you would post a video clip of someone doing either, it might enlighten the rest of us.
 The "un" prefix doesn't necessarily mean that an inverse process was applied. Often it means "not" or "not yet".  For instance, your county home ec agent will suggest making sure the eggs you buy are uncracked.
Unshelled to my ear is hopelessly ambiguous. But even without 'un,' what to make of shelled oysters, shuck corns, skinned potatoes? - which of the binary states is better?
It comes to the basic principle of the adjective: to describe a special feature. The problem is when it offers a binary choice, and the 2 features are also more or less equally special, that is, rare or desirable in someway, then -
If "shelled" means "taken from their shells", then the manufacturer undoubtedly intended "unshelled" to mean not shelled. Â But as you say, it's difficult to be sure in any particular case. Â It's kind of like "unraveled", isn't it?
unshelled, unpasteurized, unwed, unmarried, uneducated, unspoiled, unknown
I guess unshelled belongs to a class of particples (which function as adjectives) that mean "have not yet been subject to the action implied", or that indicate the opposite of a binary state (e.g, shelled/not shelled, married/not married, etc.). However, it is understood that these cannot be verbs; you can't "undo" the action (you can't un-educate somebody!):
But how about unravelled, undressed, unwound, untied, unbuttoned, unzipped, unglued?
The teacher in me would explain that these are states in which a previous action has been reversed. These are also participles which can also be used in active verb forms (Please untie me).
BTW... how DO you ravel something??