63V and 63C trim codes

[Innuendo]

As I said, the code changed but the trim didn't, why?

Because it was the same colour only the pattern changed.
Using Buckskin as the colour example:
Earlier HZ had Buckskin long grain and was called 63V
Later HZ Buckskin sandpaper and was called 63C

You need to have different codes to order parts when replacing.
That shouldn't be too hard to understand?