ZD says CY doesn’t keep as long as CS. That’s changed. I seldom have CY spoil these days (and I almost never get Golden Flow). Of course, if the store doesn’t keep it refrigerated properly (or you don’t) or if you purchase milk near its expiration date, any milk can go bad. I think the expiration date on milk is much further out than it was 30 or 40 years ago, at least in the NYC area.
FWIW, I’ve seen Pride of the Farm at the Inwood Stop and Shop, for a price that’s way more than local kosher stores charge for milk.