GDPR (General Data Protection Regulation) compliance is a continual process, not a one-off activity.
Your organisation must follow the rules set out in the Regulation and keep appropriate documentation that proves you’re following those rules.
You must also carry out regular risk assessments to determine if your circumstances have changed, in this case you will need to update your data processing processes and documentation accordingly.
One such change of circumstances is Brexit. As a result, there are now two versions of the Regulation: the EU GDPR and UK GDPR.