A user downloads an Account from Opendata through Network Account Search (NAS). If there are custom fields in the customer's Network instance whose values are automatically generated (for example through Network Expression (NEX) Rules or Alternate Key generation), the values of these custom fields do not get downloaded into CRM automatically, even though they are mapped in Network Administration. When are these values downloaded into the CRM org?
As the custom fields do not exist in Opendata, only standard fields get downloaded by NAS, and the Data Model rules set in the Network instance (NEX Rules, Alternate Key value generation) come after this. The next Full or Delta Target Subscription job updates these values in the CRM org.
CRM Help Documentation: Network Account Search
Network Help Documentation: