If it smells ok and tastes ok; it's ok to eat. If you're suspicious of either of these then throw it out

no

Do it all the time if it hasn't been opened. But agree with Monita go with smell (and common sense).

It may depend on the nature of the yogurt. A good naturally fermented yogurt, without a lot of added ingredients, unpasteurized, will slowly continue the fermentation process. To me this means that it is safe and may be more tart. The big no-no with yogurt is contamination , often from a spoon which has been used for other ingredients or used in your mouth, dipped into the yogurt container, which will turn up with various colored molds when you open it later. Keep it clean and the yogurt will be good for a while past those dates -- which I consider a scientific fiction.

I used to only eat it, like any dairy, unsealed for 7 days. But my friend keeps it indefinitely and she's a chemist. I'll eat it up to a month if it looks and smells okay.

I find that the texture of greek yogurt changes when it's no longer good. for some reason, I have had better luck with regular yogurt.