As to your second point, the “large amount of interpretation” you mention is actually a dispute between the Rama and the Shach. (This article fully explains the halachic situation.) To summarize, the Rama posits that general supervision is enough to make cheese kosher; the Shach requires active Jewish participation (i.e. physically adding the rennet) to make cheese kosher (gevinat yisrael). In the 1800s, the Chochmat Adam sided with the Shach (strict), and the Aruch Hashulchan sided with the Rama (lenient) but encouraged following the Shach. In the last century, R. Moshe Feinstein adopted the view of the Aruch Hashulchan (lenient okay, but strict encouraged), and R. Zushe Blech (who has worked for the OU, cRc, and MK) indicates that the generally accepted practice is the stricter one. So, it would seem that in normative Orthodox circles, there isn’t much disagreement.

In either case, the ingredients are the same; it’s the participation that matters! So it’s not surprising that the OU can do a special commercial run of Cabot cheese in a straightforward manner, as we saw with the “Shapes of The Cape” crackers.

But in its day-to-day operations, does Cabot adhere to this stricture? I haven’t the foggiest. But I choose to live in a particular community with a particular rabbi, and I trust his decisions on what’s kosher and what isn’t. So for me, an OU heksher means I can eat — and so do a lot of other widely-known hekshers. I’d be happy if Cabot chose any of them, and they’re certainly free to choose.

I’m more than a bit concerned these days about the nature of larger certification agencies such as the OU. As far as I can tell, there is exactly nothing different about the Cabot cheese that went into the package either before or after the OU symbol was added – the OU already had certified some of the larger/commercial packages of the same cheese. Interesting, huh?