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I assume this was to do with the primary (and almost sole) use of Ronald Syme's Augustan Aristocracy. However, this is justified, as Syme's book is pretty much the only book (English language at least) that discusses (or mentions in some cases) most of these topics. This is mainly because Syme's book is so comprehensive that there has been no need for anyone to write a similar book (or else no one else is really in any position to 'compete' with Syme and his book).
As such, asking for further references is a fruitless exercise, as they don't exist.