It is ok to bill the subsequent code -
Here is what it says in the CMS manual.
Contractors shall not find fault in cases where the medical record appropriately demonstrates that the work and medical necessity requirements are met for reporting a subsequent hospital care code (under the level selected), even though the reported code is for the provider's first E/M service to the inpatient during the hospital stay.
Unlisted evaluation and management service (code
99499) shall only be reported for consultation services when an E/M service that could be
described by codes 99251 or 99252 is furnished, and there is no other specific E/M code
payable by Medicare that describes that service.
Reporting code 99499 requires submission of medical records and contractor manual medical review of the service prior to payment. CMS expects reporting under these circumstances to be unusual. T he principal physician of record is identified in Medicare as the physician who oversees the patient’s care from other physicians who may be furnishing specialty care. The principal physician of record shall append modifier “-AI” (Principal Physician of Record), in addition to the E/M code.
Hope that helps