Is this proper format?

[Scott]

https://www.goodreads.com/series/8886...

Down at the bottom, some collected works say "includes book x.x", which generates odd and confusing series text on the book pages.

It should just be the number, right? I've never seen this used before.

[Sandra]

I've seen it before, but I personally always just use the numbers.

[rivka, Former Moderator]

Such notations are acceptable, although most librarians do not add them.