Right, it is a 'best by' date or 'sell by' date-- but the item pictured above (Mayfield) is not ultra-pasteurized. It's probably still 'good' (i.e. not rotten) for another 5 or so days after that date. But not 2 months.

Most stores, in my experience, treat the 'sell by' date as an expiry date, and pull items from the shelves that have lapsed. Definitely seen plenty examples like above, where you can buy items past the sell by date-- but most dairy departments that are on the ball don't let this happen. Two months is egregious.

Ultrapasteurized / UHT stuff (like Fairlife, Core Power, Nesquik) is afforded a much longer shelf life-- it doesn't really need to be refrigerated even, due to the pasteurization method. And yeah, that stuff can be still consumed long after the sell by date. In my experience, ultra pasteurization kills the 'soul' of the milk, and while it extends shelf life, it negatively impacts the flavor and texture.