According to Jain tradition, Bhagwan Mahavir’s Janma Kalyanak (birth) is celebrated every year based on the tithi (Chaitra Shukla 13), not by counting a “running year” like 2525th, 2625th, etc.

About His birth year:

• Shwetambar tradition: Mahavir Swami was born in 599 BCE. ( jainknowledge.com)
• Digambar tradition: Mahavir Swami’s birth is placed in 615 BCE (some Digambar sources give slightly different years, but 615 BCE is most common). ( jainknowledge.com)

So, both sects are celebrating the same tithi (Chaitra Sud Teras) as the Janma Kalyanak of Mahavir Bhagwan, but they differ on the exact historical year (599 vs 615 BCE).

You can read a simple explanation here and about Mahavir Janma Kalyanak here