There are three different ways the diary duplicator can copy dates over to the new year.

1. 52 Week - Copy dates over to the same day of the equivalent week, shifted 52 weeks forward.
2. 53 Week - Copy dates over to the same day of the equivalent week, shifted 53 weeks forward.
3. 1 year - Copy dates over to the exact same date shifted exactly 1 year forward.

The difference between these can be made clearer with an example.

Assuming an original date of Thursday 24th of August 2017

1. With "52 weeks" it will search forward 52 weeks and then add the event to the equivalent day of the week: Thursday 23rd of August 2018
2. With "53 weeks" it will search forward 53 weeks and then add the event to the equivalent day of the week: Thursday 30th of August 2018
3. With "1 year" it will simply add the event to the equivalent (or closest matching) numerical date in the new year: Friday 24th of August 2017.

To illustrate this here is the original date on a calendar view:

Now here are the updated dates, shifted forwards one year, using the three different methods: