I've seen this question a lot lately. You need to check with your local carrier. My local carrier, NHIC instructs coders to give full credit for a Comprehensive history if the information is unobtainable. Here is the exact quote from NHIC:
Here's the link
Think about it, if the patient is rushed to the hospital, unconscious, no family present, and cannot provide a review of systems - why should the physician be limited to a level 1 admission?? That seems like a pretty serious case, I wouldn't be surprised if the provider felt it was a level 3 admission.... but without a detailed or complete ROS technically it doesn't even meet the requirements for a level 1 admission.... so keep that in mind.
Same applies for Family history. If the patient was adopted and cannot provide the physician with family history, don't fault the physician for that. Give them credit for checking, even though they were unable to obtain the information.