Fix bug related to coordination numbers

When deducing the century of a coordination number the normalized form must still be a coordination number. I.e., the day component is still increased by 60.

An example from the test cases (with a reference date of 2017-12-12): the coordination number 171270-0002 should normalize to 20171270-0002. Before this fix it was instead normalized to 20171210-0002.