I agree that distinguishing between all late Vasart and early Strathearn is difficult, if not impossible. But from several conversations with Catherine née Ysart, who used to grind bases for Vasart, I get the impression that whilst some Vasart bases were ground on a wooden wheel with abrasive powder, giving the characteristic marks, that did not happen for early Strathearn weights.
If so, that suggests borderline weights with a ground pontil are most probably (?definitely) Vasart. Flame polished bases could indicate either. Does that fit with your understanding, or am I making too much out of scant evidence?