is b category registration starts after A category counselling completed

For exams like NEET or JEE, there is an All India Quota (AIQ) for central institutions and a State Quota for seats within each state. The counselling process might have separate phases for:

• A Category (AIQ Seats): Counselling for filling seats under the All India Quota might happen first.
  
  
• B Category (State Quota Seats): After A category counselling is complete, counselling for filling seats under the State Quota (B category) might commence.
  
  In some universities or institutes, there might be a single counselling process with merit-based selection. Candidates from all categories (including those who didn't participate in A category counselling) might be considered together based on their marks/rank.
  
  I hope it helps!