Normally I would not respond as I have not decided how to proceed as we develop.
The 75 L24 gun (type on the Stug75* and PzIV75) did have a Canister round that contained 960 small steel balls. Appears the 75 on the PzIIIN which was slightly different did not have a Canister round. Note that the 75Ls for example would not be able to fire a Canister round due to having a muzzle brake.
What I have not found (at least yet) is anything that confirms a basic load of Canister for these vehicles.
Conversely, have found that many Russian tanks/guns had a basic load of Canister rounds, thus the C#s on various vehicles from BFP.
Generally everyone used Shrapnel/Canister rounds in WW1, but most abandoned them during WW2, or at least after the early war years as these were comparatively expensive to produce. The US and USSR are the exceptions.