The basic rule with lifters is "when in doubt, throw them out". You can put new lifters on a used cam, but used lifters must go back on the exact same lobes they were removed from, preferably in the same engine. Even then, you should check the lifter bottoms to make sure they still have some "crown" by placing the base of one lifter against the side of another. It should only touch in the middle with daylight visible around the edges. If they are dead flat, or dished, chuck them. If you do find any which have much dish at all, take a good look at the corresponding cam lobe. The lobe should be ground on a slight taper, but the nose should be flat across. That is, if you place the side of a lifter (or any other handy straightedge) across the nose of a lobe parallel to the cam, it should contact the lobe straight across with no daylight visible at the edges. The rear edge of the lobe will be slightly taller than the front which causes the lifters to rotate and keeps the cam from walking forward-backward in the block with the engine running. Many times it's a lifter that wipes out a cam, not the other way around.
