I'm pretty skeptical of this. I'll put some comments below.
"I do have a rough theory how about AU points are awarded, but it’s so different from the fico algorithms that you and u/beefy1357 and I and others are familiar with that it’s controversial, to say the least. Here are the broad strokes as I understand them:
There are no negative reason statements associated with not having an AU card. Points awarded for AU cards exist outside of the well-known scoring metrics and are strictly awarded as a bonus. I don’t believe this is controversial, but the rest of my working theory becomes progressively more so.
No negative reason statements for not having an AU doesn't imply that there are bonus points for having one. From what I've seen, an AU card, if not discounted by anti-abuse algo's, only adds what that card would add to a profile if it were a card under that consumer's responsibility. As an example: When I added my wife to my aged Disco, she had no open revolving or any revolving history, her score jumped significantly. When she added me to her a-few-months-old Disco, I had a thick and aged profile w/ about 15 years of revolving history, and my scores didn't do anything. This is just what you'd expect to happen if those cards were our own. The only unique scoring I've seen demonstrated for FICO8 that has to do with AU is the AU AZ penalty.
I believe there is a sliding scale for the size of an AU card award based on the individual’s current scores. As an example, someone with fico 8s in the low 700s will see more than twice the bonus points for an AU card as someone with fico 8s in the low 800s will. I have quite a bit of data on this, because of the way the Authorized User All Zero penalty is calculated. It is very easy to determine the size of an AU bonus if you know the size of the AU AZ penalty, which can be determined at will.
From this, I can't see that the poster has isolated the effects of their hypothetical sliding AU bonus from the different effects of adding an aged revolver to different profiles. Many profile in the low 700's would have more to gain from adding an aged, low util, etc card than profiles in the low 800's, regardless of reported responsibility.
If I understand the last line of this paragraph correctly (I'm not sure I do), I think the poster is saying that the hypothetical AU bonus is the same as the AU AZ penalty, and that you determine the one from the other by their being equal. I don't see a reason to think that's the case (the effective bonuses for 1st-3rd bankcards are not the same as the AZ penalty, for example), and I see a good reason to think it's not the case: If you add an AU card to a profile that receives a sizeable bump from it, and then report AU AZ the next month, you likely won't see a drop equal to the previous gain. (This makes me think I'm not understanding this poster, but I'm not sure what else their claim that AU bonus can be determined from AU AZ penalty could mean, since they seem to think their reader would know what that method of determination was without their giving a means of calculating it.)
I further believe there is a sliding scale for the size of an AU card award based on the qualities of the card (age, payment history, credit limit). I don’t have any concrete knowledge about how this scale operates, but I have noticed this: despite the fact that AU cards don’t contribute to aging metrics but do contribute to UT, both age and credit limit are essentially equal in determining the size of an AU card award. Optimizing both is best for the largest award, but there is a limit. I’ve personally witnessed that a 29 year old card with a $54,000 limit does not give a larger bonus than an 20 year old card with a $41,000 limit. Even a 15 year old card with only a $18,000 limit essentially maxes out the fico scoring bonus and is enough to give someone with no other credit history an EX fico 8 above 740.
Again, where this poster sees a "sliding scale", they could just be seeing the different effects a tradeline can have on different profiles. I also don't think that a hypothetical, complicated sliding AU bonus that both does and doesn't score from AU account age is the most parsimonious explanation for different cards having different effects on different profiles, since the difference in profile may be enough (though more info about each profile would be needed to say).
Info in the last two sentences of this paragraph is incomplete (e.g. limits are not scored in themselves, only util), but I think the poster is saying that they have seen a cap on how high an AU card will push up the score of a thin or otherwise empty profile. If there is, it could be the case that there is a cap on AU contribs specifically (e.g. all AU 15yr+ score as 15 yrs for aging), or the poster could just be seeing scoring limits for thin profiles that would be the same whether or not the cards in questions were AU (again, more info about the profiles and the testing the poster performed is needed to evaluate their claim). Neither requires a separate AU scoring metric that uses different logic from the rest of the FICO8 algorithm.
I only have the most basic understanding of how a single AU card can give someone with no other credit history a fico 8 of ~750 and how 2 AU cards can result in ~780. I’ve witnessed this phenomenon myself, and I’ve read countless posts about it happening. My working theory (if you can even call it that) is that the AU card acts as a proxy revolving account; the presence of a revolving AU credit card satisfies the open revolver requirement. This seems to differ from all of the other data I’ve observed about AU cards - it’s somehow related to the classic fico scoring algorithms that we’re all familiar with. This is also the reason why I believe 3 AU cards (and nothing else) is worth even more points, but 3 AU cards when you have other open revolving accounts doesn’t result in additional points.
Again, I don't see a case for why this behavior is different from the difference in score gain you would see from having, e.g., 3 vs 6 open revolvers on different profiles. Not enough information is provided to know if they're properly controlling for AU anti-abuse exclusion or independent changes in scored metrics.
There are other peculiarities about AU cards that I’ve picked up over the years, but they’ll only confuse my answer even further, so I’ll leave them for another time."
Hopefully this poster will provide more detailed information about their methods and DPs so the FICO-pondering community can better determine the merits of their view.
