The board marks are used to check if the candidate has met the required minimum aggregate in Physics, Chemistry and Biology/Biotechnology based on their category. The relation between NEET and Board marks pretty much end there. Later during the counselling, you are asked to submit the marks lists as proof. The admission into Medical colleges either through All India Quota or State Quota is based on your performance and qualifying status in NEET. Its just not with Tamilnadu, but with every State. Please go through this link for more information: https://medicine-careers360-com.cdn.ampproject.org/v/s/medicine.careers360.com/articles/tamil-nadu-mbbs-counselling/amp?amp_js_v=a2&amp_gsa=1&usqp=mq331AQCCAE%3D#referrer=https%3A%2F%2Fwww.google.com&amp_tf=From%20%251%24s&ampshare=https%3A%2F%2Fmedicine.careers360.com%2Farticles%2Ftamil-nadu-mbbs-counselling