Keith Nuttle wrote:
I have three computers
The computer names are lap, desk, tablet.
lap and desk are running Windows 8.1, and tablet is running Windows 10.

The account names are the same; MS account, John Doe, and the local
account, John Doe2.

Would this prevent one computer from installing MS updates and apps
from the Windows store?

Software installations are done into "trees" owned by TrustedInstaller.
No ordinary user account would own such a folder.

And TrustedInstaller isn't a regular account. For example,
TrustedInstaller doesn't have its own home directory. So
you won't see a C:\users\TrustedInstaller or similar.

Programs stamping files with TrustedInstaller ownership,
use a "token". One way to get the token, is by impersonation.
A program run as Administrator, if programmed properly,
can get the token. Which is a rather circuitous route to
stamping such file permissions.

What that means is, many times, the user can "steal"
ownership from TrustedInstaller, but the user can have
a devil of a time putting it back the way it was.
One way, is to record the permissions of the entire C:
into a text file, using icacls. And later, play them back
and reload the C: partition with those permissions. So
icacls has the ability to repair permissions of everything,
but you have to be prepared in advance. And any files
added since permissions were recorded that way, would be
missing from the playback file operation.

The Windows Store has wsreset.exe to use, to attempt
to repair the folder used as a cache for Store downloads.
I don't know all the duties of that program, whether it
is clever enough to make the cache folder owned by
TrustedInstaller again or not.

For Windows Update, there is the SoftwareDistribution
folder. You do "net stop" on two services, then
empty that folder, then "net start" the two services
right after that. That's probably what the
Control Panels :Troubleshooter might do, if you
selected a Windows Update repair option in there.

Your problem should not be related to user account name
choices. Even if you were "George" in Windows 8.1,
and "Ringo" in Windows 10, that should make no difference
to the folders owned by TrustedInstaller. And for Administrator
to correct an incorrect ownership, the same impersonation
procedure is needed, whether the folders are owned
by "George" or "Ringo".

I have no idea, how Windows Store purchases for
"George" and "Ringo" are recorded on the system. The
wsreset.exe program, it cleans the cache, but I don't
think that has anything to do with validating previous
purchases or downloads. The cache should fill itself
again, according to whatever file or registry entry
records the details of that nature. Presumably that
would take a miniature database of sorts. It would
make a mess of the registry to store a small file
for each store purchase. So there should be an
actual separate database (Jet Database?) for it
instead. There are people who will load up with
500 copies of Angry Birds, and the design has
to have storage space for that sort of thing.
And peppering the registry with authorization
strings, wouldn't scale very well.

If you actually lost the authorization information,
presumably even that is traceable to an account
on the computer. But it would not be "George" or
"Ringo" local accounts. It would be traceable to
a MSA (Microsoft Account). That's my guess.
The database file itself might be owned by
TrustedInstaller, but the strings stored in it,
would key off the MSA used to make the purchase
or orchestrate the download operation.

It's quite possible you didn't do anything to
antagonize it, so don't give up hope.

Paul