1964 Penny, 2 Coin Extra Spine Growth Progression

Hi SP67,
I'm confused by your reply. You indicate the "extra spine" is a double die but in the link you sent SPP-Ottawa states:

This is the 1964 Extra Spine, which also occurs on coins through to the 1970s. This is probably a weak point in the design for the reverse die, which produces a crack. I have never seen longer ones, or extended cracks, though...

I am aware that there has been on going speculations for a few years regarding the 1964 Extra Spine and if it were produced by a die crack, tooling mark, or if it is a doubled die variety.

I have done a few overlays and came to the conclusion that in my opinion, it is a doubled die reverse variety.

When a working hub is pressed against a blank working die during the hubbing process, the working die has somewhat of a cone shaped face that gets flatted down with each hubbing impression (usually 2 impressions), which means that the centre of the reverse working die (the die that strikes the coins) is actually the highest area at the time.

If the working hub is lightly pressed against that high point in an incorrect orientation or angle (leaving a minor restricted impression of the spine in the centre) and than adjusted correctly and hubbed a second time, you will find a doubled spine like in the photos.

As for the "progression" the OP posted about, you can see that the doubled spine in the first image is not in the exact location as the doubled spine in the second image.

From what I can see, the OP has 2 different doubled die reverse varieties with an extra spine, not a progression.

What made me come to this conclusion is 2 things.

1. There are more than one type of extra spine for 1964 which means more than one working die used to strike the coins were affected (rare for accidental tooling marks on a random working die, unless intentional)

2. If a die crack were the culprit, there would have been plenty of examples found that show the progression by now. A potential "crack" that big would most certainly have larger relatives floating around.

Again, that is just my own opinion after studying and examining numerous examples.

DBM,

Extra spines happen on more than just 1964, they have been found across a few years, all looking identical, or very similar to the ones the OP has shown, which is not common for a random crack or accidental tooling marks.

there were over 480 Million 1964 small cents minted, with an abundance of working dies like you pointed out, and only a handful of those working dies featured an extra spine with different sizes and locations present.

With that said, there are over 9 different doubled die reverse varieties for 1964, so yes, it has happened more than once for this specific date and denomination.

Just like there are over 15 Doubled Die Reverse varieties for the 1974 Nickel Dollar, or over 10 Doubled Die Obverse varieties for the 2012 Loon dollars.

Edit:

I should put it out there that my conclusion is one that took numerous days and countless hours of research and studying examples in various grades from AU to BU.

Personally, I just don't think a die crack or tooling mark is the culprit, I do understand why SPP-Ottawa made the suggestion in the 70th edition Charlton and on that post that was linked here, however that was also during a time when not very many folks were actually looking and researching doubled die varieties enough to make a solid conclusion IMO.

With that said, I do have it listed as a DDR, I just don't see it being anything else.

After thinking about this one for some time, I concur with JohnWayne. This extra spine also occurs in the centre of the coin, and the doubling is confined to a small area. A similar phenomena occurs with the doubled bud 1-cent coins and the 1974 nickel dollars.