That's a very specific and important question to ask during the CSAB special rounds. The discrepancy between what you see on the choice-filling portal and the official PDF document is a common point of confusion for many students.

Here's the most accurate way to understand this situation:

The information displayed on the online choice-filling portal is generally considered the most up-to-date and authoritative source for seat availability during the counseling process. While the PDF documents released by CSAB are helpful for reference and as a general guide, the live data on the portal reflects the real-time status of vacant seats.

Therefore, if NIT Agartala's Biotechnology branch is showing up as a choice available in your portal, it means there are indeed vacant seats for you to fill for that particular branch and category.

There could be several reasons for this kind of discrepancy:

• Real-time updates: The online portal is dynamically updated. As students surrender their seats, withdraw from the process, or have their seat allocations canceled for various reasons, those seats become vacant and are immediately added to the available choices for the subsequent rounds. The PDF documents, on the other hand, are static. They are published at a specific point in time and might not reflect the most recent changes.

• Tentative nature of PDFs: The PDF for vacant seats is often released as a "tentative seat vacancy." The document itself might even state that candidates can fill choices that are not listed in the table, further reinforcing that the online portal is the primary source of truth.

• Category-specific vacancies: The PDF might show a general overview, while the online portal will show the specific seats available to you based on your category (e.g., General, OBC, SC, ST) and other criteria like state quota. A seat might be vacant in a category that wasn't mentioned in the general PDF but is open for you to apply for.

My recommendation is to trust the online choice-filling portal. If you see NIT Agartala's Biotechnology as an option, you should definitely consider adding it to your list of preferences if you are interested in that branch and college. The goal of CSAB special rounds is to fill all the remaining seats, and the online system is designed to facilitate this by showing all possible options to eligible candidates.