Not all of the Devanagari letters are in the letters lessons 1-3, will we learn the rest after? or it's like this because it is beta?
I found some more letters in Basics 2, I believe. So I guess they are all in there later on.
I am new to Duolingo, so don't know my way around. However, I discovered accidentally that there are more layers to each of the lessons. I don't know how many layers, but I have got to crown level 3 on one of them so far. After you "complete" a lesson and get a crown on it, you can click on it again and get a whole new set of exercises. As you go through the next layer of each lesson, more of the letters are added. I presume that by the time you get to the last layer, whatever that might be, all letters will have been covered in depth.