Patty, I agree that products like meat and dairy can go bad before the "sell by date." But that can happen LONG before the sell-by date if a product like milk, meat, or mayonnaise (opened) is left in temperature above 60º for several hours.

That's one reason why I don't think dates themselves should be relied on too much.   
Eggs, for example, may be really "fresh" for only a few weeks after they are laid, since the farms are required by the FDA to wash off the natural protective covering that the hen puts on them when she lays them.*   But you can get a good idea of how fresh an egg is by looking at how high the yolk stands up.   And when an egg has gone bad, it's usually not hard to tell.   But in the case of dairy products, there's a huge difference between how long milk lasts and how long cheese (e.g., cheddar, blue) or something with live cultures like yogurt does, yet the labelling often tends to be similar.

How safe something is may also depend on whether you're eating it 'raw' or using it in cooking (at a very high temperature).

There are also some products that basically never "spoil" due to age.   Honey is the best example, but sugar also doesn't "go bad" the way, say, flour or oil will.

What I'd really like is a good index of foods and food storage guidelines for various kinds of foods and various methods of preservation (e.g., refrigeration, drying, canning).



*If that covering is left intact, eggs can remain safe and edible for many weeks WITHOUT refrigeration and for months with it, but you're not allowed to leave it on when you sell eggs commercially, because you can't assume the consumer knows to properly wash the egg right before cracking it.