The Changchun Technique is the same; it's a type of health-preserving qi skill, similar to the Turtle Breath Technique. Unless he cultivated the Changchun Technique to a higher realm than the Turtle Breath Technique, his lifespan's upper limit was unlikely to increase.
If the same type of health-preserving martial arts could really stack, others wouldn't be fools; they would have already practiced such methods to live for hundreds of years. Obviously, that's impossible. How could attaining longevity be so simple?