K.A.
Those "sell by" dates are more about when the store isn't allowed to sell them by vs when they are good until.
I remember reading an article about this. While there are some things that really do go bad on or very close to that date, other things are good for a good long while after the fact. You can buy day old bread at the grocery store for instance.
It really depends on what it is and how past it's date it is.
The baby food jars, are the tops still air tight or have the buttons in the middle popped out or look like they are beginning to bulge? How far past the date are we talking? If the jar is intact and it's not to far off it's date I'd still use it.