Since we are writing Call Numbers in pencil. Naturally they are being written in manually. The alternative way is to copy/paste the numbers from other sources which is not desirable. I am narrating why it is so.
There is a book called WHERE THERE IS NO DOCTOR by Dr. David Werner. In my Library of an ICMR institute, the book was classified under Medical Science (610+). When I joined an ICSSR institute and purchased the same book for the Dept. of Sociology, the same book was classified under "Sociology" (310+)
So had I copy /pasted the Call No.from my previous organization, this book would have been isolated in my new Organization. Later after nearly a decade we developed a Sizeable collection on Health Economics & Medical Sociology and started running courses on that topic as we got a fairly large fund from an International Organization, for benefit of the scholars we shifted a portion of the old collection and there we put new Call No. under Medical Science for those books to be exclusively used by the people studying/ working on it.That is why we need to put call No. afresh and manually through pencil. Never-the-less, the World Bank has several publications on Agricultural Economics, Climate Change, Public Health. HIV/AIDS etc. which bear varied Call Nos in different Institutions according to their focus of Research. I had been one of the full Depository Librarians of the World Bank for more than a Decade. So you can take it as a official comment.
I am sorry for this belated reply but for last couple of months I seldom signed in to LIS Links site and that is why I missed your post.
Whatever the NAAC people say, the norm is to use pencil while writing Call Numbers manually into books and Registers. The same norm is followed in UGC Library, Supreme Court Library, BSI Library, National Library and even NAAC Library if they have one!! The one and most vital reason is FLEXIBILITY.Every now and then, the Universe of Knowledge is being enriched. Earlier (in the 60's) automated activities were classified as "SERVO MECHANISM" If you have access to old editions of DDC, you can check my statement. In the pre 60's period the term "Molecular Biology" was not available in Schedules. The term "Molecular Epidemiology" is not available in DDCs published before 1992-3. The Human Genome Project was initiated in the year 1991. Now the point is, when we were unable to put specific call No. in the past we had to use broad Class No. now with the advent of new knowledge when we can get brief and compact exact number, we have to use that number. We have no choice. It is natural therefore that using pencil is the only way out to make necessary modifications of the Call Numbers without spoiling the Register pages.
In our University, we use pencil and I am expecting NAAC visit to our University shortly. I am eagerly waiting for an encounter with them.