Most late Roman emperors after Constantine issued a limited number of types. If you get out your reference works and list them all you may find the list of AE types is short enough to aspire to get them all. However, there is usually a very rare type or two that will keep you from finishing the set. Five years ago Gorny & Mosch had an extremely rare (R4) AE4 of Jovian (363-364) that I had never before (or since) seen offered. I just checked and it is still the case that none are on acsearch or CNG. I thought, if I could get that one, completion of a type set was within reach because Jovian issued only four AE types (not counting mints, etc -- just types) and the other three are commonly available.
So, I bid much higher than I might have otherwise and won the coin. Then I put together my site on AE types of Jovian:
http://augustuscoins.com/ed/Jovian/Jovian.htmlConsider the same thought process with another emperor, Constantius Gallus (351-354). If you collect late Roman coins or seek one of each ruler, you know that his most common type is FEL TEMP REPARATIO soldier-spearing-fallen-horseman. In fact, it is the type of more than 90% of his coins offered. If you only want one, you can be done with one soldier-spearing-fallen-horseman. However, do you know what else was issued in his name? (Probably you don't care.) I went looking and found ten AE types in RIC VIII. I think one very rare listed type is actually an unintended mule, so that brings it down to nine official types, with two further varieties of significant interest. Could I get them all?
No. A few are just too rare--too seldom offered. But, I can tell you what I learned about AE of Constantius Gallus. I can list and illustrate the types on a web site:
http://augustuscoins.com/ed/Gallus/Here is a recent acquisition which is on the page:
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25-23 mm. (Large) 5.53 grams.
Emperor standing left on galley, holding victory on globe crowning him, with left hand holding standard with chi-rho, galley steered by Victory holding a rudder.
III in left field, * in right field. ΔSIS in exergue.
RIC Siscia 329
Near the bottom of the page there is a table of frequencies. It shows the "galley" type, which is common for other emperors, is on only about 2% of all Gallus coins. Unfortunately, there are five types rarer than this one that make it unlikely I can complete the set. So be it. There are lots of other coins to desire and lots of other web sites to write. In the process I'll have lots of fun learning about ancient coins. As our member @TIF would say, "This is fun!"
Show us a coin of Constantius Gallus!