For a coupling facility log stream, when a rebuild occurs after you update a time stamp using IXGUPDAT, the time stamp for the log stream will be set for the time of the last log block written and recovered to the log stream. This will be the last log block written, unless rebuild processing indicates a loss of data condition for the log stream.
If the rebuild occurs after one or more successful write requests have occurred since the IXGUPDAT request, the time stamp is reset for the last post-IXGUPDAT written and recovered log block time stamp. If however, the rebuild occurs before any write requests to the log stream since the IXGUPDAT request, the time stamp for the log stream reverts to the last pre-IXGUPDAT written and recovered write request.