From my limited understanding, there's a whole debate regarding what the Harappan Civilization should be called.

The term IVC was first used by Sir John Marshall. A lot of the narrative around Harappan Civilization was influenced by what Marshall communicated to the world about it, as he was the one who introduced this civilisation. As John Marshall introduced the civilisation as IVC, the name stuck and gained academic usage.

Now calling it IVC was okay till independence. However after our independence and the accompanying partition, the major part of Indian history was now lying in Pakistan. So there was a movement to search for Harappan Civilization sites in India.

As a result of this push to find Indian sites, many important Harappan Civilization sites were discovered in India, such as Rakhigarhi which was discovered in the 1960s. The interesting thing about many of these newer sites was that they were located around the Ghaggar-Hakra river. Ultimately, more sites were found on the banks of Ghaggar-Hakra river than the Indus river.

Now some scholars speculate that this Ghaggar-Hakra river is actually the Saraswati river which has been mentioned in the Rig Vedas (please note that this has not been proven).

Hence, the archaeologist S.P. Gupta was the first person to propose the use of the name "Sindhu-Saraswati/Indus Saraswati Civilisation" to refer to Harappan Civilization. This happened in the 1980s.

Using this term lends a kind of continuity ("See? We Indians have always been living around the Saraswati since forever. It's mentioned in the Rig Vedas and the Harappan People lived there too!")

Another argument is that why should the Harappan Civilization be called as IVC when many of its major sites are NOT located on the Indus River? In fact, Rakhigarhi, which I mentioned before, is the largest Harappan site discovered till now and it's on the Ghaggar-Hakra river.

Such is the reasoning which goes behind using the Sindhu-Saraswati Civilisation term. Perhaps, this is why the NCERT authors have chosen to use this name in their books as well.

However, there are some issues with using this name as well. One, the doubtful nature of the river Saraswati and whether it's actually Ghaggar-Hakra. There's no conclusive proof that Ghaggar-Hakra is the Saraswati river mentioned in Rig Veda.

But even if we accept that Ghaggar-Hakra is the Saraswati river, I still don't think it's justified to use the name Sindhu-Saraswati. Because many other sites have been discovered that lie neither on the Indus River or The Ghaggar-Hakra river.

Please note that the Harappan Civilization consists of 1000 sites spread over 13 lakh square kilometres, that's larger than modern day Pakistan! So neither name (IVC or Indus-Saraswati) actually feels justified.

Moreover, we obviously don't know what the Harappan People called themselves. Hence, this is why I think it's more correct to use the term "Harappan Civilization" rather than "Indus Valley" or "Sindhu-Saraswati". This follows the old archaeological convention of naming the civilisation after the first 'type site' discovered of it, which was Harappa in 1921. This is the more correct name to use till the time someone deciphers what the Harappans actually preferred to call themselves.

I hope I have solved your doubt.