When a condiment says "best if used by", how long after that can you use it?

I'm talking about like salad dressing, mustard, and those types of things (well, condiments!). I know mayonnaise is one thing that you don't want to use to long after that date. I have like 3 unopened salad dressings that say best if used by like June and July of this year, should I toss them? I would think they'd be fine!