That’s simply just a different counting system being used across different cultures. Some systems would count the first year of reign as being year 0, others year 1. South Korea recently used a different system to the rest of the world. So under this system if someone wrote that a child was two years old and the another wrote that they were three, but the second was a South Korean, both would still be correct.
Here’s one: direct numerical difference from one verse to another. This book is not a reliable account of (alleged) events in the near east.
https://www.lyingforjesus.org/Bible-Contradictions/when-did-ahaziah-begin-to-reign-sab.html
That’s simply just a different counting system being used across different cultures. Some systems would count the first year of reign as being year 0, others year 1. South Korea recently used a different system to the rest of the world. So under this system if someone wrote that a child was two years old and the another wrote that they were three, but the second was a South Korean, both would still be correct.