1999 Ford Explorer front bumper and grille assembly

That's a question for a body shop. They'll all have Mitchell Crash Estimating guides that will list the manufacturer's part numbers. If they're the same for both years, the parts are obviously the same, but when they're different, they still might interchange. If one is painted and one is chrome-plated, the numbers will be different. Some mounting tabs may be moved a little or they could be beefed up to address a common problem. Often that warrants a new part number. Ford generates part numbers that include the year that part was first used but you have to know how to decipher them.

You can also visit any salvage yard. They all get the Hollander parts interchange books. Those give you a code number for your part in the first section, then you go to the second section and look up that code number and it will list all the models and years that part fits.

Sometimes one part, such as the grille, will not interchange because it's shaped differently, but if you transplant the head light housings too, and maybe the fenders, all those parts together may bolt right onto the vehicle.