Is it wrong to learn more about the incomplete characters in calligraphy? Why?

There is nothing wrong. There are often some words with less or more points in calligraphy, such as running script. When writing brush strokes, the points on the upper right half are usually removed, and the word "Shen" is sometimes added to the lower right after writing. These are limited to calligraphy, but generally it is wrong to write like this.