Passing through again on my way to work ; but it occurs to me that you may have the resources Michael is really looking for, James. Because I think his question is, to what extent does the wrapper material reflect “what the church has always believed”?
You and some of the other contributors around here are better grounded than I am on arguments about the relative prevalence of universalism among church authorities (not to say popularly) during the centuries up to the rise of Islam (which is roughly where the AthCreed seems to date to, btw.)
Similarly, while I know that the Eastern Emperor Justinian II declared universalism (not just Origin’s rather heterodox notions of pre-existent souls and reincarnation etc.) to be anathema, this would hardly be something the Western church would heed (then or later), and obviously the EOx themselves, though (I suppose??) still respecting his opinion on the matter nowadays, hardly consider it to be an authoritatively dogmatic statement on par with a councilor agreement. (Otherwise they would dogmatically reject universalism as even being an option, instead of simply refusing to teach it as a dogmatic affirmation, leaving their theologians open to affirm or disaffirm it individually according to each teacher’s best understanding.)
Or anyway, this is the (quite possibly mistaken) impression I’ve picked up over the years. But other people here seem far more qualified to go into that kind of detail.
In any case: Michael, I consider the wrapping statements to be technically gnostic, and therefore heretical in themselves and not to be accepted. Unfortunately, the technical gnosticism (where salvation is a matter of knowing the proper doctrine as a sort of passcard into heaven) is prevalent throughout church history, including prior to the AthCreed, in both branches (Western and Eastern) of the church. I don’t think this prevalence can be denied; at best, someone might (though I doubt it) be able to argue that it wasn’t quite a majority belief among learned authorities (not to say popularly).
Also, my understanding is that although the EOx do not formally accept the AthCreed (due to provenance issues tracing it back to “Athanasius”, but also due to the filioque affirmation that tends to be included in it), they do recognize themselves to be in agreement with the content (minus the filioque), so there’s a real though informal agreement among Western and Eastern branches in affirmation of the theological propositions of this Creed. With the qualification of the filioque dispute, this Creed can be said to represent the last vast majority agreement position.