Why do some types get listed twice, with two distinct RIC numbers?

RIC IX has many indistinguishable types with two different numbers. It makes sense if you think about the cataloging problem. Suppose an issue begins under emperor A and continues after co-ruler emperor B is elevated and the elevation is celebrated with a new type. So, now there are two distinguishable time periods (before and after). If the continuing type is listed for emperor A in the first period, should it be cataloged with only that one first number? But that would make it seem to not belong to the second issue and make it unlisted in an issue where it was still issued. So, RIC catalogs it again in the second period with a second number, even when the coins of that type for emperor A from the first and second periods are indistinguishable.

Here is a timeline of events that distinguish periods.

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