"shelling??"
ManagedNav:
I'm not sure what school NWA techies attend, but I taught engine troubleshooting for decades to dozens of different airline & military customer groups, and never ever heard anyone use the term "shelling".
A stall or surge may or may not imply physical damage to the engine, even though a spectacular flame front suddenly appears at the inlet and exhaust. Some engines are quite prone to surges, as I'm sure you are aware since you list DC-8 in your bio; a few surges are hardly unusual on a downwind outboard JT3D in reverse thrust.
And while I have seen shrapnel damage to aircraft skin, it has always been the result of major engine case penetrations and always accompanied by severe engine vibration during the spooldown. (Most notable was a Pan Am A310 at Hamburg in 1987 - it even bent the pylon!)
I've seen no report hinting that BA had this kind of problem.