You never mentioned the S on the reverse, that would have nothing to do with the A on the obverse.
Hard to tell from that photo, a closeup such as you showed with the A would help but from what I can
see, it looks more like damage than doubling.

It would be a long shot if it is a 1921 as there is believed to only be about 400 in existence.
What makes you think it is a 1921, a TPG would not certify it unless the date was clear.

With the larger photo, I would have to say that it is a scratch on the frosting preventing it from a high grade.
Agree that it is a PL, not a SP. A 1986 Specimen would be Brilliant Relief on a Brilliant Background.

Hard to tell from small photo but it is either a small die crack or a scratch.
If it is raised, it is a die crack, if incuse, it is a scratch.

Minor die chips do not usually add or subtract value from a coin.
As far as having 20 out of 25 with chips do not make the ones
without more valuable. There were 750,000 of these produced
and the vast majority would not have that die chip.

There is no such coin as a 1878 Seated Liberty so it is a fake coin
with no Numismatic value.

Definitely damage, it is only an error if it happens during the striking of the coin
and there is nothing on that dime that could happen at that time.

Not an error, it is the edge of a tellers stamp.
Technically it is damage.

Not sure where you see an error, all I see is damage at 11.00

Welcome to Coins and Canada

First of all, what city or town do you live in.
Also are you able to provide clear photos of the coins if requested.
When you say uncirculated, that could be anywhere from MS60 to MS67

Looks like it may have been buried for a while.

All US coins between 1965-67 had no mint marks so you won’t find one with one.
Where did you get that pricing from?

Do they have lowball sets for currency like they do with coins?
This would be a perfect candidate.

It is one of a series of I believe 6 issued to commemorate the 1980 Olympics.
There were about 4 1/2 million of each produced and are made of cupronickel.
There was also a silver set produced that came in a presentation box.
Yours with the case is probably worth $8-9.00.

There is a complete listing for *CD notes in the Banknote section.