Ok. Rereading the question, let me see if we can clarify this....
"I have a patient that was admitted to the hospital through the ED. Prior to going to a room on Admit day, the ed requested Neurology to come consult. Neurology consulted, and documented their note but when the neurologist documented his note, he did not meet the requirements for an inpatient consult."
In your question you mention that he was in the ED and prior to going to the room was asked to consult. If the patient was not registered IP yet, then the consult by the neurologist is based upon the status of the patient at the time of the consult. So that would be an ED or other outpatient consult, depending upon the requirements of the patient's insurance carrier (EX: Medicare does not allow 'consults').
"The neurologist documented his note but didn't meet the requirements of IP".... Is the missing documentation about the reason, request or report that isn't included in his medical record? (The three Rs?) Or is it missing one of the History, Exam or MDM elements?
However in the CMS manual see the first full paragraph on page 60. Medicare may not be the carrier you are sending the claim for, but it is good reference information that most insurance carriers will follow as well. You can also verify in the billing manual for hospital services of the insurance company for the patient.
https://www.cms.gov/files/document/medicare-claims-processing-manual-chapter-12
As far as down coding to subsequent, it is what we learned with auditing "if an encounter lacks the needed requirements we down code to a subsequent encounter" (taken from one of my auditing manuals but no reference cited). I have yet to find this verified in CPT or CMS however. If it is Medicare, the local MAC carrier may have some requirements as well to verify.
There is always the unlisted E/M code too...