How subtle do differences have to be to be differently attributed?

[the10thlegion]

In the process of trying to identify a coin (it’s identified so not posted in the help identify section) I ran across 2 coins that to my untrained eye would be the same.
Both these coins pictured are sestertius of Severus Alexander (courtesy CNG). There are only 3 differences I see in the coins and they are so subtle I thought they were the same but the descriptions from the web site attribute them differently.
1) on the obverse the space between the N and D is different
2) one has a thin modus the other is wider
3) both are holding a “pole” type object with the arm bent at different angles

Per the descriptions on CNG there is no mention of the spacing in the obverse legend or the shape of the modus. However the top coin the pole is described as a scepter and the bottom coin as an anchor. I would have missed this difference on my own and in doing a double take yes the bottom coin appears to have a curved something at the bottom, almost touching the C in SC. I assume this “pole” is what makes the difference but I’m not sure.

The top coin per CNG is RIC IV 518; BMCRE 766; Cohen 422
and the bottom coin is RIC IV 520; BMCRE 768; Banti 109

The reason for this post is I’m hoping for an explanation on how different something needs to be to be properly attributed. I’ve seen coins much more different than these 2 having the same.
Thanks

[curtislclay]

Both of your coins are RIC 520, since both have PIVS in obv. legend. RIC 518 is an earlier variant, without PIVS.

Both coins should show Annona holding an anchor, with a curved arm at the bottom; the arm is just hard to see or was maybe erroneously omitted on the first coin.

BM 766-768 are basically three examples of the same coin; the one small difference is that 766-7 have an unbroken rev. legend, while 768 has the break X - COS. Your two specimens both have the legend break, so could be catalogued as BM 768. On the other hand legend breaks are not usually described or considered to constitute different types on coins of the early empire, so it would also be correct to catalogue both of your coins as BM 766, the first of the BM's specimens and the one illustrated on the relevant Plate 26, despite its omission of the rev. legend break which your coins show.

[Altamura]

The attribution of ancient coins is no exact science or internationally standardized  .
Already in your example you see several phenomena:

The attributions of dealers, even the most careful ones, are not always correct. They often do not have enough time for an attribution or the right people to do it, so errors can happen. (Personally I only document attributions I have seen myself in the books referred to, I never just copy an attribution from a dealer. But doing so is part of the fun I have with my coins  .)

The reference works used for attribution can be roughly divided into collection catalogs (like BMC and the SNGs) and type catalogs (e.g. H.A. Troxell. The Coinage of the Lycian League. ANSNNM 162 (1982)).

In a collection catalog each coin specimen in the collection is described and usually has its own number. And if the collection comprises three specimen of the same coin minted with the same dies then you potentially have it described three times with three different numbers.

In a type catalog the aim is usually to give an overview of all the coin types of a certain ruler, city, time span or whatever the criterion for the catalog is. Here usually a number is given to each type, and within the type there are given references to collections holding this type: https://babel.hathitrust.org/cgi/pt?id=uc1.b3897219&view=image&seq=155
How fine the distinction between different types is made is up to the author, there are no "eternal rules" to be followed.

And quite often for the attribution of a coin you have more than one reference book with different structures, different datings, different descriptions  .

With ancient coins you very often don't have unambiguousness, but in my eyes this makes the thrill  .

Regards

Altamura

[the10thlegion]

I agree with you it is a lot of fun trying to identify what you have. Unfortunately for me my library of books on ancient coins is limited , very limited.

In the response by Curtis he mentions that one has PIVS and the other doesn't. Both of you mention misattribution - think you're correct in the companies often not having enough time (and maybe someone w my skill level). That gives me more peace of mind that I was on the right track but just didn't have the resources to confirm it. My biggest mistake was assuming both were correctly attributed and that left me in doubt as to which way I should go.

Since this wasn't a help identifying question but more trying to distinguish between the two I found online I didn't include a pic of the subject coin. Later this week I'll get my imaging stuff set up and include a pic of it. But the purpose of my post has been answered - thank you both.

[Pekka K]

Actually both coins are  RIC IV 520 b (with slight drapery over left shoulder),
and this detail is different too.

Pekka K

[the10thlegion]

Here was the coin I was attempting to attribute.

Side note - this has to be the best quality pic I've ever done on a coin. Other than combine the obv & rev there was no editing done to the pic. Getting close to professional quality - maybe.

[dougsmit]

Side note - this has to be the best quality pic I've ever done on a coin. Other than combine the obv & rev there was no editing done to the pic. Getting close to professional quality - maybe.

My suggestion to you at this point in your photo 'journey' is to try to shoot this coin again several times.  Try to do everything the same once and then try to change little things - minor angles of coin or light.  After this series of perhaps a half dozen variations, ask yourself which looks better and which spoiled the mood.  Does the image look better with a little added contrast in postprocessing?  Do you recognize any differences or are all the same?  Digital photography allows playing with little things without breaking the bank buying film and processing. 

Your question is one that will cause disagreement among some of us.  I am 'in this' as a hobby.  I am not a scientific professional or a dealer.  I value mint identification by style but am relatively uninterested in such matters as letter spacing unless I can determine that this was in some way a code with meaning rather than random execution.  Is a dot just a dot or a mark of a workshop?  Can the work of two die engravers be separated by a code, a style or even an open signature?  Not all differences are equal to me and the ones that mean something to me may be totally unimportant to you or to the professional numismatists among us. 

I agree fully with Altamura:
"The attributions of dealers, even the most careful ones, are not always correct. They often do not have enough time for an attribution or the right people to do it, so errors can happen. (Personally I only document attributions I have seen myself in the books referred to, I never just copy an attribution from a dealer. But doing so is part of the fun I have with my coins  ."

I'll add: Decide what you enjoy and which differences matter to you.  Collect accordingly.

Below I add two photos of coins that are exactly the same in terms of the Cohen catalog but vastly different to  RIC, BMCRE and those who consider matters of style and mint ID.  In this case, I care.  Do you?  Collect accordingly.

First below: Rome mint RIC 11, Cohen 267; second: Eastern mint (traditionally known as "Emesa") RIC 367, Cohen 267