It's the Experian FICO 8 score offered through my Amex dashboard with the 300-850 range. A free report from Experian I pulled in May for a home lease application showed 849 and I was around 820-830 when my report was run for an autolease 9 months ago. I wasn't necessarily trying to maximize my credit score number rather was just being responsibile about eliminating all of my credit card debt I had accumulated during my training/schooling (I had a lot, but fortunately all at 0-4% interest as part of SCRA for military members).
I currently have:
15 credit card accounts (split between my wife and I) - all with 0 balance except 1 (just read about this AZEO so perhaps thats what did it)
2 student loans outstanding (2yr10mos old)
1 car lease outstanding (9mos old)
* I just paid off an auto loan earlier this month which may have been another factor that pushed me to 850?
Oldest account is 18yrs 9 mos
Youngest account is an auto lease : 9mos
AaOA is 9yrs 1 mos
Hard inquiries - 1 (auto lease)
At 1 point I had 99% credit utilization on $100K+ worth of credit cards - however I had a plan in place and end in sight (with minimal accumulated interest) so methodically reduced this over the course of 4 years. One thing I did that was helpful with utilization was to call each of the 15 cards each year and request an increase in my credit limit. This was an easy way to reduce the utilization. I'm currently sitting at 1% utilization.
Probably just a combination of luck and debt responsibility but now that I'm aware of the factors I'll likely try to maintain things in preparation for a large mortgage I plan on getting in the coming years.
My guess is the elimination of the car loan, the average age of accounts eclipsing 9 years and my utilization dipping down to 1% are the factors that led to the 850.
Do you know if the scores you were provided with outside of your Amex account were also EX Fico 8 scores? With the auto lease for example, it's possible that they used an Auto enhanced flavor score, which would of course be an apples to oranges comparison to a Fico 8 classic score. If you've had the Amex account all along and were checking that EX Fico 8 score through them, you'd see from month to month at what point you hit 850. From there perhaps you could look back 1 month (when you hadn't hit 850 yet) and see what changed from that month to the next.
The auto loan being closed shouldn't have impacted your scores much since you have other open installment loans. Moving to 1 less account with a balance may have helped a couple of points, but nothing significant.
Your age of accounts factors increasing could be it. Your AoOA already being 17+ years means you've already maxed out that factor, so additional age there I don't believe would have any Fico score impact. AAoA could perhaps, although some theorize that after around 8 years AAoA the rest is just gravy and doesn't further impact score. AoYA wise, some people see gains at 3 months and 6 months with the biggest gain coming at 12 months. I don't believe that 9 months should matter.
Utilization is of course a big factor. If you can pinpoint the time when your overall utilization moved from above 8.9% to below 8.9%, that could without question have been the event that bumped you up to 850... but that would have probably be a bigger jump up... perhaps from 835-841 or so being your previous score directly to 850, as crossing the 8.9% threshold is significant. If you were already sitting at 849 chances are your utilization was already in an ideal place and possibly something like moving to fewer accounts with a balance (going toward AZEO like you said) could have bumped you up a few points.