3) see 8.12 Ammunition Supply Chart
You know I've never looked at that chart as anything but superfluous, but is it? For example, the StuG 75/46(i) has a 75L, but has no APCR on the back of the counter. However, if the C8.12 chart applies, it has APCR as a GERMAN 75L. Of course, it is an Italian vehicle, and the notes happen to say that it has an Italian AA gun adapted as its MA, but the "German" 47L is a foreign gun (as is the German 76L) mounted on foreign vehicles (French and Czech) yet it gets APCR, so I don't think that you can rule APCR out because it isn't a "German" vehicle or gun.
So, I think you play it as only vehicles with notes on the counter have special ammo, but the rule is a bit vague. I'd recommend in ASLRBv3, the table be removed completely and just refer to Chapter H as the definitive answer.