To put it bluntly, the True Immortals after the Immortal Ascension Tribulation were immortals who had survived the three calamities.
This was because the three calamities of becoming an immortal were really too terrifying. If one was unlucky and could not survive, their lifespan might only be 500 years.
How could a mere 500-year-old immortal be considered a True Immortal?
Only after passing the three calamities of becoming an immortal did they no longer have to worry about dying because of the calamity. They could live as long as heaven and earth and shine together with the sun and moon.
Only such an immortal could be called a True Immortal.
Of course, the so-called lifespan of heaven and earth and the brilliance of the sun and moon did not mean that one would really live forever.
This was because the current Jiang Li knew that heaven and earth actually had their own lifespan.