If you edit an existing record, you look to [Date Modified] for the date of last modification. The field [Date Created] will never change once populated. Anything after that is an edit.
With the QB Actions, to create a New record in the manner you're describing, leave off he [Record ID#]. The database will always provide a new ID number to this field itself. You would only provide a new ID# to a custom Key Field.
Is the synced table related to the table the Action is pointing to? If so, you can provide the Related Record ID#.
Anytime you input to Record ID#, you're updating if the value you're providing exits.
As you may not have two identical Record ID#s in the same table, the behavior you're experiencing is valid and correct. If you should provide a value to Record ID# and that particular Record ID# does not already exist, the system will issue you an error, which is valid and correct.