USE BY and BEST BEFORE mustn't be confused.
This.
That said, with quite a few
unsweetened dairy products, they can keep for amazingly long times
if you're scrupulously careful to avoid inoculating the stuff with greeblies [micro-organisms]. Plain yoghurt and high-fat cream [45% butterfat], to name a couple.
The simplest way to do this, is to use only a freshly-scalded [i.e. well rinsed with boiling water] metal spoon to extract the stuff from the jar, and not to leave the lid off any longer than necessary. Get it back into the fridge promptly, too.
