I hope that following link and paper will be helpful.

Regards

https://books.google.iq/books?id=V9iZCwAAQBAJ&pg=PA440&lpg=PA440&dq=Is+headache+in+patients+with+hypertensive+crisis+considered+as+a+sign+of+target+organ+damage+(TOD)?&source=bl&ots=MDMu-IwG2J&sig=fk1OErrekjdAuKTLKoXAfF51kYs&hl=ar&sa=X&ved=0ahUKEwj86OqmlpzLAhVoSZoKHf4lARIQ6AEIIzAB#v=onepage&q=Is%20headache%20in%20patients%20with%20hypertensive%20crisis%20considered%20as%20a%20sign%20of%20target%20organ%20damage%20(TOD)%3F&f=false

Article Hypertensive crisis: Clinical-epidemiological profile

No. It is not considered as a sign of target organ damage. If it is associated with cerebral infarction, cerebral haemorrhage, subarachnoid haemorrhage or hypertensive encephalopathy, only then it is considered as a sign of target organ damage.

Definitely not, unless, as Dr Mohammad Ullah pointed out, the headache is a symptom of  another condition. But even in these cases, the conditions causing the headache are the signs of target organ damage, not the headache itself.

"Certain patients, independent of BP levels, present neither evidence of acute target-organ damage (TOD) nor an immediate threat to life, which obviates the need for antihypertensive therapy in the emergency room. This condition occurs usually in oligosymptomatic or asymptomatic hypertensive patients, whose BPs, although under treatment, are not controlled and are typically elevated. Another group of hypertensive patients may have a transient BP elevation caused by any emotional, painful or uncomfortable event, such as migraine, vertigo or headache of muscleskeletal origin, and manifestations of panic disorder. Such symptoms characterize hypertensive pseudocrisis". 

Sobrinho S, Correia LC, Cruz C, Santiago M, Paim AC, Meireles B, Andrade M, Kerner M, Amoedo P, de Souza CM. Occurence rate and clinical predictors of hypertensive pseudocrisis in emergency room care. Arq Bras Cardiol 2007; 88: 579–584.

Nice cohort study posted above. I looked through all the other cohorts that they reviewed and they're lacking details on the blood pressures the patients presented with. What exactly is the danger zone for blood pressure, outside of which end organ damage will not occur as a direct effect of the hypertension? The consensus numbers seem to be SBP120 but it's a mystery where these numbers came from. Zampaglione had no patients in his 400 something person cohort with DBP

You can not make a cut-off for danger zone, because it all depends of how long the hipertensive state is! It also depends on other individual factors, so the best think to do is to think in terms of symptons sugestive of end-organ damage instead of the level of hypertension! Let's not treat the mercury!!

Not really! Headache, not only a sign of hypertension, could be a symptom of different illnesses. Laboratory results and medical history of patient should be well examined and evaluated before target organ diagnosis. Thanks.

Implications of headache in patients with hypertensive crisis

Severe blood pressure elevations (hypertensive urgency) may be associated with mild symptoms (e.g., headache, lightheadedness, nausea, shortness of breath, palpitations, epistaxis, anxiety) without acute target organ injury (1).

Focal headache persisting after the BP is controlled should warrant brain imaging to rule out intracerebral or subarachnoid hemorrhage (2).

However, severe headache (thunderbolt headache) can precede coma or hemiplegia in patients with subarachnoid hemorrhage (SAH) or intracerebral hemorrhage (ICH), in such people or when the headache persists after control of blood pressure, cranial imaging (CT brain) is warranted in such patients.

1. Article Severe Asymptomatic Hypertension: Evaluation and Treatment

2. Article Headache in Acute Stroke. A Prospective Study in the First 8 Days

3.

Article Approach to the Diagnosis and Management of Subarachnoid Hemorrhage