Let's list the nations that have a 47 anything (47*, 47 or 47L).
French: Both 47 and 47L. Though the French had done some pioneering work on HEAT, I have never heard of a HEAT round.
British: Though not in British colours, the Vickers 6 Ton was British and never had a 47* HEAT round, so the various Chinese, Bulgarian or Polish ones are out.
German: Just the 47L as mounted on the PzJg I and as the Axis Minor (Slovak) 47L AT gun. This might have been what they were thinking about.
Japanese: Both as a 47L tank and AT gun, again I have not heard of a HEAT round.
Belgian: Never heard of a HEAT round.
Italian: The Italians had a HEAT (Effetto Pronto) round for their 47 and 47L tank and AT guns from '42, but what little I have found out indicates it's a calibre round, IE 47mm in diameter. That would only give penetration in the 10-12 TK range. Some at least used in the desert, some said the users were happy, some that it was no better than AP rounds in penetration except at distance. See: http://www.comandosupremo.com/forums/topic/343-47mm-4732-and-tank-gun-ep-effeto-pronto/ ASL in my opinion rightly ignores it. Ditto for the Axis & Allied Minor 47 guns of the same parentage (Böhler).
My guess is that the ASL designers had the German 47L in mind. This was a Czechoslovak AT gun and I would be surprised if they did not develop an oversized spigot type round that fitted over the muzzle. The Germans did such rounds for the 37L AT, 50L AT and the 150* INF, the later more a anti-bunker round than an AT round. They went with normal calibre rounds for their 75 and 105 HEAT rounds. As the 47L as mounted on the PzJg I only lasted in German service from '40-'41, I would be surprised if many rounds were produced and might have ended up in Slovak hands. A TK of 26 implies an over calibre spigot type round.
The "To Kill" chart features a couple of oddities, no doubt because it was designed at the very beginning of ASL before most of the vehicles with those varying armaments were even introduced into the system. A non-existent HEAT round is IMO less mysterious than the "Grant Gun" entry in the AP section. What is a "Grant Gun"? OK, with a little bit of deduction most people could probably work out that it's the 75mm gun in the Grant tank. So why does it have a different kill number? You'd expect the relevant Chapter H section to include an explanation, not to mention a reminder that the Gun uses a non-standard TK value. Certainly you'd expect the counters to include a reminder! Nope. Not a word any where -- just that mysterious entry on the TK chart.
(I know the real-world explanation for the different value -- the early version of the US 75mm gun was not as good as the later, more standard version -- but you can't expect most players to be aware of that, and to remember it in the heat of the game. That early gun was fitted to some early Shermans, too, and maybe elsewhere. Many Grants were fitted with the later, better gun. It's hard to determine the true applicability of the TK value when the rules refuse to even acknowledge its existence!)
Yeah, the "Grant" gun was the 75mm M2. As manufactured the Grants got the M2. By the time the 75mm M3 gun was available the British had ordered Shermans and the Grant was out of production. The later M3 gun got put into later Lees and nearly all 75mm Shermans. The ASL Lee gets the M3 as by the time the Lee saw service a majority of the Lees had the later M3 gun, though there were a fair few M2 armed Lees in Tunisia. I'm relying upon the relative numbers of M2 and M3 armed Lees in photographs. Only a handful of Shermans (plus the T6 Sherman prototype), mainly M4A1, were shipped with the M2 gun, the British got one named "Michael".
The M2 and M3 guns were fairly interchangeable, so maintenance requirements could end with a M2 armed Lee becoming a M3 armed one. The only difference is that when put into a gyro fitted Lee the M2 needed a muzzle break like counterweight on the barrel end to give the same balance as the longer M3 as the gyro and gun cradle combination was designed with the longer M3 in mind.