How do you know whether a place name has been standardized as intended?
Answering my own question, the simple answer is, "You don't"!
The screenshot below illustrates a common problem. In this example "North America" has been accepted as a standardized place name, but it had been standardized as "American Samoa"! Strangely, I found (when I accidentally stumbled across this) that top of the drop-down list was "North America - Continent", so I easily switched to this. Incidentally, the "North America" had been carried across during the attachment of an England & Wales census source, by another user.
I have often encountered examples like this (usually by "accident"), but short of checking every place name entry that appears to have been correctly standardized (i.e. no Data Warning message / red exclamation mark) I don't know how you could ever monitor the "match" between the display name and the "hidden" name to which it has been standardized.