In general, fields sent within Update messages are always a subset of the fields you will see in the Refresh message. So, if you see FID 975 ACT_FLAG1 within an update, you will also see it within the Refresh.
When you subscribe to data, the Refresh will contain the complete relevant set of FIDs associated with that asset. This will be the first message you receive when you ask for the data. When there is activity in the market, you will begin to see updates and only those FIDs that are affected by the market event will be updated.
Hope this helps.