I would pitch them.
in your statement you did mix terms in the description<<<<< you mentioned that they may have been necked down, and then referred to case length,,,
If they were trimmed or cut down,, it would reduce length,,,
If they were "necked" down, they would have a smaller diameter.
anyway,,, it's not worth the potential problems to fiddle with them,,, and who knows why somebody would invest the time to alter 9mm cases to work in 380.
The case specs are pretty much identical other than case length.
When reloading, always remember, conservative is better. Why take the risk ? You spent good money on,,,,, the reloading equipment, your gun,,,, and you and your parts aren't replaceable conveniently !!
keep shootin straight