It depends. If you are well versed in ML then you know the concepts very well and have already played with them extensively. Thus reading a paper might be enou

It depends. If you are well versed in ML then you know the concepts very well and have already played with them extensively. Thus reading a paper might be enough to learn it because you have done all the conceptual work up front. But even if you didn't learn the papers you still have built a mental catalogue of ML results that you can go back to learning when the occasion to implement them arises. So yes, you probably learned a chunk of them and some you simply remember, but that's ok.