How to identify A1, A2, etc. reading material?
I've downloaded a boat load of German readers. They are supposed to be mostly A1 and A2, but except for a few of them, none have such a label on the cover or inside.
The vast majority are from Langenscheidt and many do use a "Stufe" notation, 1, 2 or 3. These could be referring to their own level system, however.
Is there any way I can sort these out between the levels? By correlating them to the ISBN or just examining the vocab and grammar?
A1 and A2 are both still very much beginner level. A1 will consist of rather short and easy sentence, whereas A2 will venture out a bit further, but it still shouldn't get too complicated. Just look at what Duolingo covers in the first half of its course and in the second half. Although there will not be a complete 1:1 correspondence, it should give you some idea about the level.
Langenscheidt's level 1 might comprise A1 and A2, who knows...
Is it so important to know the level? Just try them and find those that fit best your current level: not too easy, not too difficult.
The CEFR levels are not prescriptive in terms of actual grammar or vocabulary at any given level. They just give generic descriptions of the sort of skill and type of situation that a learner at a given level is expected to cope with. It is a subjective assessment, not an objective one. I suggest you look at the official CEFR website, and try to judge from that description.
However, if you are using them to prepare for an exam, contact the examiners to understand their interpretation of the rules. No two seem to be the same for any given level / language
Here are the offical descriptions of the levels A1 and A2 from the Council Of Europe (owners of the CEFR standard) site.
A2: Can understand sentences and frequently used expressions related to areas of most immediate relevance (e.g. very basic personal and family information, shopping, local geography, employment). Can communicate in simple and routine tasks requiring a simple and direct exchange of information on familiar and routine matters. Can describe in simple terms aspects of his/her background, immediate environment and matters in areas of immediate need.
A1: Can understand and use familiar everyday expressions and very basic phrases aimed at the satisfaction of needs of a concrete type. Can introduce him/herself and others and can ask and answer questions about personal details such as where he/she lives, people he/she knows and things he/she has. Can interact in a simple way provided the other person talks slowly and clearly and is prepared to help.
As you can see, these are wide open to interpretation!