Not an error or a cud.
It is caused by a pin head sized die chip in the chrome plating on the die that expands
over time from continuous striking causing that effect.
There would be many more like this out there.

No. The extra sale is just one of the approximately 13 different varieties
of that Toonie. It would cost more to grade than what it is worth.

Nice photos but it looks to me more like a Die Crack progression that has turned into a Die Break.

Possibly gas bubbles that have broken. It appears that there is a small hole in each one.
No matter what it is, it’s not something that would be considered an error.

Wouldn’t be a planchet flaw or an error, looks like there is something on the coin.
Are those spots raised or incuse.

Cannot tell what grade from those photos, they are too dark to see any detail.
I usually store low value or regular coins in 2x2’s.
For silver or higher value coins I store them in Leuchturm square coin capsules
with the black foam insert from Lighthouse to help prevent toning.

The 1942 Tombac dies were all produced from the same master hub. It is possible that a working die when worn would produce a slightly different strike but this is due to die wear and is not a variety. I am sure that after 80 years if there were different varieties that they would have been discovere...

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.