I was working through level 1 and 2 with lots of repetitions but now on level 3 I feel I am being asked things I haven't been taught.
I find it fun to try and figure the things out that haven't been taught yet - like a puzzle. Keeps it interesting.
Sometimes I have the impression as well. But I see that as an early training for the future, where you have to know how to handle such situations in real live. Where others are not only using the words you already know and you still have to cope with it.
I think part of the reason is also that they don't want to have to resort to the "Dick and Jane" (for nonamericans three letter words level) level of teaching the language. I have found that they stick in words I don't know in places where it is multiple choice or where I can hover to see the answer - or where I need to type the spanish they provide verbally which is a good way to learn the sounds of letters.