@ptrblck , thanks for your answer.
I finally found that indeed 35 was the actual number of classes of this dataset. In my opinion it is strange that this is not explicitly written in their paper but I might be wrong since I am not an expert of ML/DL.
Here is where I found the answer to my doubts: Bitbucket (the code from the paper)
So, now, in your opinion, I should train my network with a number of classes of 35 but I should make sure that the model outputs 35+1 logits. Could you tell me why the +1? I know it is trivial but could not get it immediately. Thanks!