Any written document or manuscript of the contemporary time period of the historical figure under research constitutes Primary evidence, which in traditional Indian research was known as direct perception. Inscriptions are also valued as primary evidence. The artifacts and objects of the same time period come under indirect perception in traditional Indian parlance. We deduce the history of the person from them also.
This does not apply to the biography of Ramanauja. Nor were the Srivaishnavites of the times of Ramanuja known for having said anything that is not true. They did not hide the unpleasant episodes in the lives of Alvars like Tondaradip-podi Alvar. The famous episode of Kulasekara Alvar putting his hand in to a pot of snakes with a declaration that he may be bitten by the snakes if Srivaishnavites had erred is the test of honesty and truthfulness of the Srivaishnavites of those times. Anymore proof needed to say about the integrity of those in the status of acharyas?
Coming in the traditional way, the author of Yatiraja Vaibhava had written the panchanga details of the birth time of Ramanuja in 6th and 7th verse. Let us check if they all fall in line together. This also helps in arriving at the exact date of his birth.
Pingala, sun in Chitra (Aries), moon in Arudra, Thursday and Sukla paksha have tallied. But the tithi is shashti that follows Panchami. When we check the details we find that Panchami was running at sun rise. The common practice is to recognise the tithi at sun rise. So this cannot be treated as false information. That is the way the people had recorded the tithi at birth and the author had repeated it. The birth details given in Yatiraja Vaibhavam are accurate and the date in the Gregorian calendar is April 10, 1017. The accuracy of the birth details as tested from the astrology software is proof of reliability of Yatiraja Vaibhavam as the prime source to know about Ramanuja’s life.