Yes Pete, this is the case.
There were some countries in the World that did not demand an outer rearview mirror when our cars were new. France and Italy were among them, and I believe Spain too. Not sure about Switzerland but very well may have been.
Later on during the sixties or early seventies rearview mirrors became mandatory in these countries and "anything" was mounted just to fulfill the law.
That's why you found "unusual holes" to be filled in.
Best,
Achim