Question:

How can there be DateTime field dated before the CreatedDate on a record?

Answer:

The CreatedDate field is standard Salesforce audit field which captures the time the record was created online. 

Veeva Objects like Call and Data Change Request have DateTime fields that track changes when the action is performed offline which can be before the call is synced. Some objects have Mobile_Created_Datetime_vod__c which can be used to compare instead of the CreatedDate field.

For example, a user Creates and Signs a Call Offline which captures the Signature_Date_vod__c at that time. The user waits a few days before submitting or syncing. The CreatedDate is captured at the time the record first successfully syncs offline.

Related Documentation:

CRM Help Documentation: Sync Overview 

Thank you