As per GDPR, you will need to communicate to your clients/prospects how long you intend to store their data. AD now gives you this option. In your account settings you can set up ActiveDEMAND to align with your strategy. In the account settings your can set the length of time AD will store contact data. In the account settings, under the Account Setup tab, 'Keep Contact Data For':
Setting this to anything less than forever, AD will purge contact histories older than the time range.