Group Sid (description and domain) attached to every file

[Witis]

At the moment I am using GetFileSecurity, GetSecurityDescriptorGroup, and LookupAccountSid to get the group information attached to a file (via the sid).

I tried creating a couple of files on a stand alone machine and realised that the default seems to be:
Group: None, Domain: (The computer's name)

I looked at some system files e.g. C:\Program Files (x86)\Windows Defender\MpClient.dll and the results were:
Group: TrustedInstaller, Domain: NT SERVICE

The questions I have are:
1. When a new file is created will the group always be None, and the associated domain always be the name of the machine?
2. Is the group and domain ever likely to change over the lifetime of a file?