It was never an obligatory document because in the past there was only one way to consider the “starting point” of the citizenship’s application i.e. the date written on the first card.
Now, there is new law. It means there is an alternative way to apply for citizenship in addition to the old fashion way i.e starting date is the date written on the first card. Under new law, CdT is “must have” document. Although IRN do not accept it as part of application, whoever takes advantage of the new citizenship’s law must obtain CdT beforehand. (Note that whoever uses the old fashion way - date of the first card - will never need CdT).
Why?
What happens if the citizenship’s application is refused by IRN under the reason that 5 years of residency has not been met? If you have the CdT in hand, you can obviously bring this to court as a solid ground to fight back. Therefore CdT is the ultimate protection/weapon you should have to fight against the demons.
Moreover, if you really want to attach this CdT as part of the citizenship’s application. There are some ways. If you apply via lawyer online, then your lawyer can add this CdT as a last page of one document. INR officer will see it for sure. Alternatively, if you apply by post/by person/via lawyer, you will get the Process Number for your citizenship application. Then, you write a letter to IRN indicating that this is your process number and in this envelop there is a certified copy of CdT and you have the original copy. Use the signature of recipient required mail, IRN must receive it. It is also a way to remind them that don’t even dare to disqualify the application for not having satisfied 5 years residency requirement.