MS has a range of drivers from v15 to v27 for the Radeon HD 6570, but somehow only v15 works

Would anyone know why?

To be sure, the driver does install, and it looks right in Device Manager. But you soon find that you have only a few resolutions. You eventually notice, the problem here:

To be clear, that is NOT the installed adapter.

I tried every major version on that page: 21, 22, 26, 27, and they all have that problem Only the very bottom one, which is the only 15, works.

My HW ID: PCI\VEN_1002&DEV_6759&SUBSYS_E193174B

v15's INF doesn't get any closer than PCI\VEN_1002&DEV_67xx.

All the others do get to: PCI\VEN_1002&DEV_6759

So I don't really see why v15 would have the advantage. In fact, when installing it was the only one which warned that it may not be right.

This HW ID matches to AMD Radeon™ HD 6570.
The last W10 drivers are here: AMD Radeon™ HD 6570 Drivers & Support

You should the AMD drivers first, before trying the Windows Update versions.

I think I did start with the OEM back in the day, but it was upgraded by WU to a slightly newer version. That OEM one is also a v15.x.

I don't know why there's a huge jump of versions between v15 and v21 and above, but maybe that signaled some kind of generational shift. Maybe there were different generations of 6570's, in essence, and the "old" ones can't go past v15.

I looked at that v26 you mentioned but it's the same as the v26 I tried, stopping at 6759.

In many cases, the problem is now you get driver sets, instead of individual driver packages. And depending on who's writing the external description, it's generalized as "supports XYZ model". The only thing you can trust by searching the INF file inside for your exact HWID.

That isn't to say a driver which loosely matches your base HWID isn't going to work, but nobody's around from the OEM's QA team to let you know if that's true or not. At least with the last official driver installed, you can go back in Device Manager and revert to this version if any of WU's suggested updates don't work.