As long as you've kept the Greek Yogurt refrigerated or even frozen the Expired Greek Yogurt can be safe to eat.
Just make sure it smells good and has no mold or anything else bad growing in the Greek Yogurt and it tastes good and it will be safe to eat.
Just because the Greek Yogurt has expired or has went past it's use by date doesn't mean it's bad to eat it.
If it smells bad or has a bad taste or any mold in the Greek Yogurt then throw it out because it could make you sick.
I freeze all types of yogurt including Greek Yogurt and eat it well past it's expiration date and it's always kept good in the freezer.