GMP Committee response
Annex 13 provides the requirements for IMP reference and retention samples in paragraphs 36/37. It is not clear within you question which elements you are looking for more detailed information on. The annex is not explicit about storage conditions, but these are expected to be in accordance with the product label.
The reference to 2017/1569 is not effective at this present time. It will only be effective once 536/2014 is made effective and is subject to the transition period.