Misplaced dates (MPD) make up approximately 500 varieties of all US coinage produced from 1840 to 1908, with Indian cents their prime example. During this time frame dates were sunk into dies as a separate step in the minting process and many theories exist as to why so many appear in denticles and, to a lesser extent, other locations. One theory is the date punch was used to check the hardness of the steel on a random die out of the annealing furnace. Another suggests the punch was dropped, and made a very light impression in the die. A third theory is that some inherent alignment problem existed with the machinery used to sink the dates.
As mentioned, a huge majority of the MPDs exist in the denticles and classify as minor examples that usually add no value to the coin except to Indian Head afficionados. When they appear in offbeat locations like the 1897 S1 "1-in-neck" they add a large premium to their market value.