‘C’ is a special char here. All codes must start with it, leaving the rest grouped in two groups: numbers, then letters. X Y Z is a pretty common placholder for ‘11’ ‘12’ and ‘13’. ‘C’ will also function as a clear button, to begin entering a new code attempt. Probably why they chose ‘C’ as a simple label.

I may have gone with left to right then top to bottom, instead of top to bottom then left to right; but that’s more personal preference.

https://codelocks.zohodesk.eu/portal/en/kb/articles/cl100-cl200-2018-code-change-instructions

From my experience with mathematics, algebra, and calculus, C is a representation of analogous data storage. This means the C is the button used to change the coding. A better way to identify it would be to consider it as “clear” or “cancel”. So like you put the wrong code in, use the C to start the code over