Multiple entries in contacts birthday calendar per person

Please help us by providing the following info. Before posting please also check the pinned "Known issues" threads and make sure that you're running the latest available version for your oC release:

Steps to reproduce
1.There are two or three entries in contacts birthday calendar per person
2.There is a single contact which contains birthday information for each relevant person in contacts (there may be an entry for some people in multiple addressbooks though, but only one contains birthday information)
3. Addressbooks have been deleted and recreated for various reasons

Expected behaviour
One entry per person

Actual behaviour
Two or three entries per person, unable to delete the extra ones.

Server configuration
Operating system: Debian Jessie 8.7
Web server: Apache 2.4.10 (Debian)
Database: Mysql 14.14 Distrib 5.5.54
PHP version: 5.6.30-0+deb8u1
ownCloud version (see ownCloud admin page): 9.1.4 (stable)
Updated from an older ownCloud or fresh install: Updated
Special configuration (external storage, external authentication, reverse proxy, server-side-encryption): None

ownCloud log (data/owncloud.log)

Please paste possible errors in the following code block, see for more info

Integrity status for oC9+

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paste the results here.
No errors have been found.

I presume the entries get added each time a contact is found with a birthday. Once that addressbook is deleted, the entries aren't removed, so adding and removing addressbooks leads to stale information. How can I remove the additional entries/refresh the contacts birthdays calendar?

There is a occ command allowing to resync the birthday calendar:

Thanks. I ran the command and unfortunately that didn't remove the duplicate entries, the good news is it didn't add any either.

If I delete the calendar, does running that command recreate the contacts birthday calendar or do I need to manually do that myself?

Thanks again for the help.

OK, I answered my own question.

Deleting the contacts_birthday calendar via the web interface, then running the occ command that kljhlkhglklfgh pointed me to recreated the birthday calendar with a single entry per person.