It weighed in at 2.6 grams, is much thinner, and has a rough edge, with no rim. It fits perfectly in a dime cut out sleeve. The picture isnt detailed enough to show the edge ,Which looks flat and smooth except one portion looks slightly caught/sharp.However , the rim is rounded down not up, with the L in Liberty angled exactly to match, and Lincoln ispressed through the other side.
Quick question - how does the size compare to a dime? The rough edge you mention (but I can't make out in your picture) leads me to believe that someone shaved it down. I've seen cents shaved to dime size to try and pass for dimes in older coin operated machines. Also could just be someone with too much time on their hands. You can always check the coins that the mint produced for other countries during that time. I don't have the list handy right now but I know it's out there with a bit of google searching.
Interesting and valid observations, however what stands out for me is the way "In God We Trust" and the L in Liberty appear to roll over the edge of the planchet. I feel this would argue against the shaving hypothesis.
No. It's most likely damaged. Find out what foreign coins the mint was making that year, size weight, metal composition. Philly 1971 there is a list that will tell you if they were even making any foreigns that year. If it is the same size as a dime (yet its copper) it is unlikely to be a foreign planchet as foreign coins are deliberately not the same size and weight as US coins. Too many You Tube videos recently about foreign planchets and missing clad layers.
When a Blank Planchet is struck the words don't roll over the edge. It's some kind of post mint damage.
Looks like it was squashed too in order to make Abe not as high profile relief. the hardened steel die isn't going to "flex" to roll the words down around an edge. looks like someone was trying to save 9 cents.
I find your reasoning contradictory. A planchet of the correct size would not have the rollover, but if the planchet were smaller than the planchet that was intended for the strike, the words would roll over the edge, as it does in this case. As to it's worth - I have no idea. If it is indeed a mint error and not post mint damage, an error collector might be willing to pay a nice sum. It's all in the demand.
I'd tag an error expert, except we'd be wasting his time … but I recommend you ignore all of us and send it to PCGS for grading.