Hello Ole,
The issue seems mostly solved.
In Outlook.com contacts, I had to remove manually a number of duplicates.
It seems the records which were not cleaned up automatically are the ones which had no name/surname in Outlook 2013 but only a company name and ¨file as¨ filed populated.
I have lost many contacts with this problem.
I´ll have to import my saved contact list from Outlook 2010 and will hopefully recover most of them.
Thank you very much for your investigation and support to the benefit of the community.
Cheers,
Serge