Prabhupada told early ISKCON artists exactly what some vague shastra details looked like, and we have our evidence in ISKCON paintings. So any ambiguity is resolved for us in terms of what Krishna looks like, dresses, and so on. Am I so mistaken about this?
This argument quickly breaks down. Prabhupada approved many paintings with features that are different from Shastra. Here are a few examples:
1. ISKCON art has a dark-haired Narada. The Bhagavatam says he is blond.
2. ISKCON art has a dark-haired Indra. The Rg Veda says he is blond.
3. ISKCON art has a young Srivas in the Panca-tattva. We know that Srivas was an elder in the community, not a shaved-up young devotee.
4. ISKCON art shows the gopis with modern Indian saris. The Bhagavatam says they wore belts, not visible in ISKCON art.
5. ISKCON art shows royal ladies with saris. The Maha-bharata says they wore belts and an upper and lower garment, not visible in ISKCON art.
These are just a few examples. In each case, Prabhupada approved ISKCON art that does not agree with Shastra. Keep in mind that the Acaryas you refer to all come from a very narrow historical period. We do not have a lengthy history of Acarya claims. Your view that Acaryas are describing Krishna 5000 years ago, rather than their internal visions is simply that — your view. I respect it but do not agree with it.