The original scenario gives the Stuarts Canister and HE, by SSR. The counters don't until 1944. Does anyone have any info as to whether Russian Stuarts would have Canister and/ or HE during this time frame? I don't know if the SSR was added for balance purposes, or if the designer knew something Chapter H doesn't.
I won't argue the rules because the RB did not cover that particular detailed aspect of British posing as Soviets.
The initial M3s (94?) may have come from British stock or from the US but originally allocated to Britain and reallocated to the USSR. Most seem to have been delivered direct from US stocks. That's Zaloga's opinion in
Soviet Lend-Lease Tanks Of World War II. I would be utterly surprise if the Soviets did not get HE, it's something they most likely would have insisted on. The Soviets produced only small numbers of the T-34/57 and possibly a handful of KV-1/57 as they felt that the smaller HE round for the 57mm ZiS-4 was more of a disadvantage despite its superior AP penetration as compared to the normal 76mm F-34 gun. They noted that the vast majority of tank targets were not other AFV and that experience is reflected in most nations tank units usually having in the order of 1/3 AP and 2/3 HE as the default ammo loadout. So for historical reasons I would say "Yes" to HE and "Quite Possibly" to C.
The British suffered, until they got Grants and Shermans, from a pre-war doctrine that tanks were supposed to mainly fight other AFV with their guns and soft targets with their MG. They were the odd ones out.
OK, so it's not in the rules, but HP has 4 x Stuart III (37LL, 2/4/2) counters with C6 on the back and the 37LL is NOT underlined. Even the Yugoslav Partisan M3A1 has a non-underlined 37LL but with C3. As both of those are after WoA, I take that to mean that both Soviet and Partisan have unlimited HE and C6 and C3 respectively and their counters override any RB guessing. Also no date superscripts to either C# or the implicit HE.
I suspect that the SSR was to ensure that historical factors would override any possible mistaken extension of British nationality traits to Soviet useage.
EDIT: I almost forgot, the Soviet Stuart III with a C6 corresponds to an "allied to US" usage, being 1 less than the US C7. If the Stuart III was "allied to British" then it would have been C5, 1 less than the British C6 (which as "allied to US" is also 1 less than the US C7).