Keith,

There is quite a bit out there I don't know and I make plenty of mistakes; but I don't go around telling people they've got it all wrong without checking definitions. I prefer to avoid embarrassing myself that way.

It is not what I am calling them. It is what they are according to the accepted period definitions. Shell and case are differentiated by whether they contain some sort of shot/fragments inside.

Adding shot changes them from shell to case even if the same external projectile body is used. Case was intended as anti-personnel air burst and was ineffective in the ground burst role that shell was often used for.

Bonus #1:
A definition that is even more obscure is that grape and canister are classified as a form of case-shot in period literature (such as Benton's "Ordnance and Gunnery.") Spherical case-shot represented a third type of case-shot and became synonymous with it--so much so that when we now say "case shot" we don't mean grape or canister.

Bonus #2:
Case fired sans fuze (so that it exploded as it was exiting the muzzle) was referred to as "rotten shot." This was a last resort substitute in a tight spot when canister had been expended. It's the same principle as canister, but the burst charge could damage the bore or even explode the piece.