Looks like the earlier gunned version (provided the change isn't merely an error or a revision) should be used in scenarios designed to draw units from the Panzer Grenadier counterset, i.e. PG, Heroes, Tank Battles etc. Probably ought to have a second listing for the lesser gunned version of the counter. More research to follow.
There is a StugIIIf, and c through e's for that matter. The IIIf's started rolling off the assembly lines in March of 1942. They had the same gun as the PzIVf2, the 75L43, which is a 5-8 on the tank. In September the StugIIIf/8 is being produced. It is a StugIIIf with the 75L48 gun, which is the same as all the PzIV's after the f2's. By November of 1942, all the StugIIIf's have been converted to the f/8 standard. So I suggest using the 5-8 versions from April-May 1942 until Oct-Nov of 1942, then use the 6-8 versions.
AP did something similar with the Soviet 76.2mm field guns when game switched from rev 2 to rev 3. Something I pointed out on Consim a while back.
I like the special rule for Soviet 76.2mm in Kursk --- because of poor coordination they must spot their own target hex (no leader spotting allowed for them).
I was referring to AP changing the bombardment strength from 12 to 10. Essentially they dropped 76.2mm gun fire groups 1 column between the HoSU counters and the Rtb counters.