The coin previously referred to in this thread has been determined to be a post-mint forgery.

That's an incredible error but how the heck can this possibly happen?

Thats An Awesome Error !!!

I would have left it in the OGP as most of these manufacturing errors from 50 years ago are loose or slabbed in the wilds.

Wouldn't be exceptional if this was Type II Ike was struck over a 1975S Type I Ike ???
My eyes make me wonder if this is the case...

Seriously, I do wonder if 1976S Type II struck over Type I 1975S is what I am looking at ???

1975S Type 1 $ reverse compared to 1976 Type 2.
The tops " LL " in DOLLAR are distinctly different.

Thats the die detail that jumps out at me on your FUN discovery flip over double strike Dollar.

I am certain, this cool error is even more interesting !

Both.
First strike in collar by Type 1 die pair(1975), then hand fed again into striking chamber flipped over & restruck by Type 2 dies,(1976).
Is this Ike available or coming up in auction ? It would fit into my error archive.
Should have cracked out of a 1976 proof set.

I see you are teaching ANA Seminar class.
Considering taking it again, been 35 years since I took it from Fivaz & Stanton.
I'm still local, so no lodging required. Been a long time since I have been tempted by a Summer Seminar offer

You bringing any epic show & tell errors for the class ?

As to the quality of the people working on the Proof set assembly line in the mid-1970's, and how it might reflect upon their hypothetical ability to recognize an error coin coming through, a story.
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One of the Authenticators who proceeded me at ANACS in Colorado Springs before I got there in 1978, so we are talking 1976-1978 here, told me about a VIP tour he had gotten of the SFAO during that period. During the tour some Supervisor was telling him how the workers, wearing masks and smocks and gloves, assembled the sets by hand, placing the coin in the inserts face up and rotated properly before the filled inserts went on to the plastic case assembly and sealing station.
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As they are walking down the assembly line, they came across a person who, between sets, was sticking the gloved hand they used on the coins into an open bag of potato chips and then, using their other hand to pull down the mask, shoving the potato chips into their mouth. The gloved hand then assembled another set.
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The Authenticator was laughing as he told me the reaction on the Supervisor's face. He thought the guy was going to explode. They hurried out of the room and somebody else took over the VI_P tour.

TD

@Mr Lindy said:
1973D Mint Set Only Issue Ike $ struck on incomplete punch planchet.
1 of 2 incomplete punched 1973D $ known & other one is slabbed, no longer in OGP.
One of my favorite errors, sourced via Fred Weinberg's website.

I fall more and more in love every time you share that set, Lindy.

I have a bunch of minor clips in the government issued packaging, including a 1970-D Mint Set Only half with a rim clip. I also remember selling member Broadstruck (RIP) a proof set with a double-clipped 2002-S Sacagawea Dollar. There is also a Mint set from the mid 1970s with a nickel on a cent planchet, I remember it auctioning in the late 1990s. For that matter, nobody caught the 1990 No-S proof cents either.

Again, the workers assembling these sets are not moonlighting as quality inspectors, and if defects are not actively being looked for, they are not going to be seen.

Sean Reynolds