(1) Regarding 中上級, my understanding was the same as l'électeur's translation. In other words, it means "intermediate and advanced level".
I think many Japanese including me understand about the level of learning and training in any field as follows:
It is common to distinguish the skill in three as "初級", "中級" and "上級" in many cases. In this case, when distinguishing the upper level from "初級 beginner/elementary level", we call it "中上級" instead of "中級と上級". Needless to say, "中級と上級" is correct, but "中上級" is easier to pronounce than "中級と上級".
I'd never doubted this understanding until I read the questioner's question.
As I read the question, I felt a little uncertainty to my understanding, so I tried to search on the Internet with the keyword of "中上級".
At first I found a site that is using this word at a certain tennis-wear shop.
Here, players are divided into five levels according to the skill of tennis as follows: 初級, 初中級, 中級, 中上級 and 上級.
Obviously here, "中上級" is not the meaning of "中級と上級", but it is understood that it is the level between "中級" and "上級".
The usage of "中上級" of this shop is not a mistake at all, but I think it is an exception when thinking in general.
In the explanation here about magazines for people who learn Japanese clearly use "中上級" as the meaning that is understood by l'électeur and me as follows.
『中上級のにほんご』は、「初級を修了した日本語学習者が、読む力、理解する力、日本を知る力を養うための素材」として作成された月刊誌。"中上級のにほんご" is a monthly magazine published as "Japanese learners who have completed beginner/elementary level read, understand and develop the ability to understand Japan."
(2) Regarding 出ている, it means 出る defined as follows in jisho.org here.
6. to appear (in print); to be published; to be announced; to be issued; to be listed; to come out
Aside from "中上級" used in the strict sense as the fourth group by the tennis-wear shop, the expression with "中上級" collectively representing "中級と上級" has, I think, two nuances.
"中上級" in the questioner's question or "中上級" in "中上級のにほんご" quoted by me is used as a word collectively referring to groups other than "初級".
In this case, they are widely targeting from intermediate people who have just graduated from beginners to people who are quite good at Japanese, so the level of contents described in texts or magazines are neither too difficult nor too easy, so it can be imagined that careful ingenuity that can be accepted by people of at a certain level and also at a wide level is being done.
In this nuance, I think that the expression "中上級" is more natural than "中級と上級".
There is the expression "小中学生" or "中高生". The former clearly points to "小学生と中学生 elementary school students and junior high school students", and the latter clearly points to "中学生と高校生 junior high school students and high school students".
For example, when you say "中高生", it clearly refers to "中学生と高校生 junior high school students and high school students", which is not used instead of "小学生を除いた生徒 students excluding elementary school students" collectively, so "大学生 college students" are not included in it.
I am going to show an example sentence where "中上級" clearly(?) points to "中級と上級" as follows.
"中上級クラスの皆さんは初級クラスの人と違って既に勉強/練習の仕方は分かっていると思いますので、各々のレベルに応じて各自適切に勉強/練習してください。 Hi, you guys who are members of 中上級, not of 初級! I think that you already know how to study/practice for yourself, so I expect each of you to learn/practice properly according to each of your level".