About base26 encoding

[Nanyan]

Hi bro, I'm confused about base26 encoding. I saw that A=00 is mentioned in the readme file, but A=1 is defined in many other places (https://geniidata.com/user/poshi/rune-index here mentions using " The bijective base-26 system", and The bijective base-26 system is defined (A=1, B=2, C=3, ..., Z=26) https://en.wikipedia.org/wiki/Bijective_numeration #The_bijective_base-26_system).
Which definition is correct?