All proofs for this year have what appears to be the loop of a repunched 8 in the lower left part of the lower loop of the last 8 in the date. On most examples this feature is easily visible. Many examples also show strong horizontal die lines in both loops of the last 8.
The first issue to cover for the 1878 proof is that there is no 1878/7 overdate. It is most likely that the curved figure in the lower loop and the strong die lines in the upper loop of the last 8 were at one time mistakenly thought to be the remnants of an erased 7 underdigit. In Walter Breen’s Complete Encyclopedia of U.S. and Colonial Coins this overdate was listed as #2439 saying it was actually the very earliest die state of next (which is the 1878 Proof). Obvious remnants of crossbar of 7 in upper loop of final 8, shaft of 7 in lower loop.
Then, interestingly, in Walter Breen’s Encyclopedia of United States and Colonial Proof Coins, 1722-1989, which was published a few years later, the overdate is not mentioned. Maybe by the time of the writing of the proof book it was confirmed that the overdate was not an actual variety. The listing for the 1878 Three Cents in the proof book does start off by mentioning that some have second 8 filled. Those with both 8s clear may be from a repolished or more worn state of the same die. This seems to confirm what we see on the existing examples of 1878 proofs studied so far. Most clearly show the strong die lines in the upper loop of the final 8 which at first look, does appear to be a filled loop.
This whole issue of disputing the Proof 1878/7 is covered very well in The Authoritative Reference on Three Cent Nickels by Kevin Flynn and Edward Fletcher. In the chapter on Unusual Varieties they present a half page on the Refuted Proof 1878/7. In their analysis they point out that there are no signs of a serif outside the final 8, which would be expected if this was an overdate. They show photos of a 1878 proof showing die scratches in the loops of the final 8. {Note: they mistakenly call them vertical die scratches when they are actually horizontal in the pictures provided}
So now that we have put the whole overdate issue to rest lets begin our study on diagnostics that have been observed on several examples of 1878 proofs. Our first coin is in a PR64 PCGS holder and has our inventory #369. It is covered in a very light toning and has a few scattered tiny specs. There are some hairlines under the toning in the reverse fields. The bust on the obverse and the wreath on the reverse have fairly strong cameo contrast. Here is a picture of both sides:
Some 1878 proofs come with the reverse rotated clockwise to about the 12:30 clock position. In Allan Giffords book, The Ultimate Guide To Three Cent Nickels, 1865 To 1889, the proofs with this reverse rotation are designated variety number P01b. In this book the circumstances involved with the filled digit and the die lines in the loops of the final 8 are explained very well. Below is an example with the reverse rotation in a PF65 NGC holder and our inventory #328.
Below is a closeup of the date area on #369, the PR64 PCGS example under study. The arrow is pointing to the semicircular curve in the lower left of the lower loop of the final 8, which is believed to be the remnants of a previously punched 8.
The date position is well centered but the base of the 1 is slightly closer to the top of the denticles than the bottom of the last 8.
An interesting feature pointed out by Breen in the Proof book is that the two eights are the same size but they are smaller than the 1 and the 7. It can be seen that the 1 and the 7 are the same size and both are taller than the eights.
Each of the digits is positioned in the following manner which is shown with the lines added.
The tip of the curl is over the center of the last 8.
The left end of the base of the 1 is over the left side of a denticle and the right end is over the left edge of the denticle.
The center of the first 8 is left of center of the denticle.
The center of the 7 is over the left edge of the denticle.
The right sides of the last 8 line up with the right side of the denticle below.
In a close up picture of the 18 in the date some raised areas can be seen in the upper left part of the lower loop of the 8. This was probably caused by the same operation that made the strong lines in both loops of the final 8. It has been suggested that some repunching was being removed and left these features inside the digits. We cant know for sure but this raised area in the first 8 in the date has always been seen in the examples that I have examined.
Now we see the final 8 in the date in a close up where the curved line and the horizontal die lines are easily visible. The curved line is marked by the three lowest arrows and then the other arrows above point out some of the stronger horizontal lines.
One diagnostic for the 1878 proof that I have always noticed but have not seen mentioned before is a pair of long criss-crossed die lines right in the middle of the bust. One line is vertical and the other travels diagonally from the chin to the top of the hair and they cross on the cheek in front of the hair just above the ear. The center arrow of the five shown points to where the lines intersect and then the other four arrows point to the extensions from there.
This feature is very easy to notice on the 1878 proofs. Here is a closeup of the intersections of these two long die lines on the cheek. The upper arrow is pointing to the vertical line above the intersection point. The lower arrow is pointing to the diagonal line below the intersection point.
There are two pairs of crisscrossed die lines in front of the lower eyeball. The pair closer to the eye is stronger than the pair near the edge of the nose. The bridge of the nose on this later die state example has been polished away and is open to the mirrored field.
On a different 1878 PR63 PCGS seen below, that is in an earlier die state, the bridge of the nose is weak but still visible. Notice the crisscrossed die lines close to the eye are clear but the other weaker pair close to the edge of the nose are not visible. The bridge of the nose always seems to be in some state of being polished away on proofs of this date.
Some very easy to find diagnostics can be found in the lower hair by the back of the head. There is a very large die chip towards the back of the hair even with the height of the earlobe. There is another die chip, not as large, a little further in the hair and a little lower. Very noticeable as well is a diagonal die line across the innermost corner of the back of the hair. All of these seem to be present on all 1878 proofs.
Now on to some reverse markers for the 1878 proofs. The isolated leaf tip above the right ribbon end is connected to the leaf cluster above by a diagonal die line.
On the second lowest leaf cluster on the left there is a strong squiggle shaped die line on the middle of the inner most leaf. At the tip of the vein in the center leaf there is another lighter squiggle shaped die line extending to the right.
Finally there is a really strong die chip in the middle of the lower half of the main leaf in the topmost left leaf cluster. This picture is taken from a raw proof in my collection.
In conclusion, the 1878 Proof has many diagnostics to look for on both sides. Some variation can be found in the amount of polishing done and sometimes a rotated reverse die.