Well, let's not get into which marriage stands valid in real world. Let's just go by the sequence of events that happened in show's timeline.
1. Anupre unknowingly got married in front of Durga maa - dhaaga shaadi
Anu - married, Pre - married, Komo - single
2. Anukomo got married in front of society without sindhoor - Sindhoorless Shaadi
Anu - married, Pre - married, Komo - married (?)
3. Pre barges in as first wife, claiming her rights, well justified by the makers, thus nullifying anukomo marriage
Anu - married, Pre - married, Komo - single
4. Komo supposedly dies, hence no debate about validity of anukomo marriage
Anu - married, Pre - married, Komo - single and dead
5. To fulfill prerna's wish of social marriage, Anu wipes off her sindhoor and pulls of the dhaaga, thus nullifying Anupre marriage (kind of divorce)
Anu - single, Pre - single, Komo - single and dead
6. Anupre get engaged. But before they get married, Pre-Bajaj get married in the temple - call it deal or blackmail marriage, however it was a complete, legal and valid marriage.
Anu - single, Pre - married, Komo - single and dead, Bajaj - married
7. Bajaj divorces pre, thus nullifying their marriage
Anu - single, Pre - single, Komo - single, Bajaj - single
8. Anu again fills sindhoor in pre's maang in front of Durga maa - divine marriage again
Anu - married, Pre - married, Komo - single, Bajaj - single
9. Anupre are about to get socially married again and Anu faces an accident.
Anu - married, Pre - married, Komo - single, Bajaj - single
Now the question that remains is why komolika is saying she is first wife of Anurag? She clearly is not, she never was. Back then too, komo never claimed to be the first wife but social wife. By the end of the track, komo had kind of accepted to herself too that pre was Anu's first wife. Now where is this first wife claim coming from? Just because Anu nullified Anupre marriage in the later stage, it doesn't make the marriage void-ab-initio and even if it does, there is no reason komo would know it.