Hi Ariel, thank you for your question.
I’m not sure how our newer version was made but the old version was made by me.
You can see on either side of the Castle Black stairs (The first image you posted) identical patterns of wavy white lines of snow blocks, which is a hint to how it was created.
First a relatively small section of the wall was made (using both WorldEdit and hand detailing) which was then copy and pasted side by side until they reached the full length.