Recovery: Who got rolled back

We had an error in our AIX shutdown procedures and the Informix instance was not being shut down cleanly prior to a system reboot. When started again, the recovery processes indicated that transactions were rolled back. but didn't say which one's. Since the reboot occures during off hours very few people were actually connected. I've used onlog to examine the log at the time of recovery and only see completed transactions (ie, begin, work, commit) at the time. Is there a way to determine what transactions were rolled back? PS. Why doesn't Informix put some sort of marker in the transaction log indicating that the instance started? You can sort of figure this out by a checkpoint record, but that might be one of several during that time period.