1972 S Cent Date Is Doubled Died? And 1971 D Kennedy Half

That's a interesting Clipped Planchet you got there.

ive never seen an edge where the brown alloy jumps from obverse side to reverse side

Correct. Note the devices are reduced in size from a normal set of devices. Usually you can tell this better on devices that curve. Like the 'D' on your image.The flattened area (MD) on that device shows the over all correct size of the device. On the areas flattened, you can see the reduction of the device turning it into one color on those areas. It is all one color on the affected areas, because the contour of the device is now missing. Where it would normally show a light to darkness shad color, it now shows as a flattened/reduced area that is all now just one color. That is how you can tell it is MD. Again on the image above, the doubled die the image on the right shows two sets of contour on that device.

The stronger the spread of the hub doubling, the more distance between the two hubbings that are noticed on doubled dies. The die is doubled, not reduced during the strike like you find on machine damaged strikes:




Machine Doubling on the same device just alters the normal sized devices by reducing them:

If the coin is worth more than $100, then you might want to slab it. Then you will know for sure what grade it is. So when you sell it you won't get a kick in the pants or give someone else a kick in the pants that buy the coin. You get an aprox grade from using the PCGS coin grading images:
https://www.PCGS.com/photograde/
Keep in mind that a scratched coin/damage/bent problem coin will not grade as high because the an issue with the coin. Some graders will often give a 'Genuine' grade on the slab if the coin has a cleaning or what other issue that they body bag a coin for. You can pick the selections to find your type of coin. Pretty easy to see what ball park it would be in. But probably a gold coin would be worth grading.

Looks like a die crack, often referred to when it goes through Lincoln's head as a "spiked" head.

You check to see if it is listed on Cuds on coins site under 'crack heads'?

Tootilliciuos!

ebay and P.T. Barnum = "There's a sucker born every minute". Some buy these "error" coins having become convinced by the hype of rags advertising becoming independently wealthy from coins in your pocket. As you've discovered, these are quite often found in circulation, that means "common" "errors". I emphasize those words purposefully. . The moreommon a coin is, the less collect ability it has, less worth. The error is a common machining problem caused by normal wear, not wholly a striking "error" such as Broad strikes, or off-center strikes which are one-of-a-kind errors. Errors as cracks, Cuds and cruds(my term) will replicate "similar" impressions, either progressively worsening or being removed with die maintenance. The frequency of the crack, Cud, crud errors makes for interesting differences and surely is collectable for those few interested. It is my view it it a numismatic fad. These errors have been around since coins were first made, why just now is it being touted as a moneymaking venture? The Shield nickel series has many of these very errors due to the hardness of planchet destroying dies. Only now, have these coins become in high dollar demand. Ah, but as with Bell bottom pants and Afro haircut, the "fads" die out, things return to normal...maybe...