A lot of the articles I read in the first year ended up being a bit irrelevant as my project developed. By the end of writing I had a "core" of about twenty articles which were really useful, and which I knew really well. Of course, I cited many other sources but it is not really necessary to remember every article you read!

It is good to hear you had a core of about twenty - I also find I have a small group of articles that have truly influenced my research, and a large group of others that either back up the same points or make minor additional points. I do sometimes worry about not including sufficient references to show that I've read around the field properly, and find myself trying to shoehorn others in!

I'm in the same position in that the components of my research each have a small core of about thirty articles, although that does mean I have about 100 core articles...

I have never used software for referencing or source management, so I'm sightly hesitant to start now but I'll have a look.

It's when I find (very occasionally!) that I've printed out the same article twice that I start to worry, especially when the first version is crammed with my marginalia. Hope I'm not alone in this!

I spent a week or so coming up with ideas and planning/reading around a topic for a new study in my PhD. It was sort of going OK and I had some good sound ideas. Then a few days later I found 2 pages (undated) where I'd outlined most of the ideas, references, and really good clear thoughts about it all. I was so shocked. It was as though I had amnesia. Couldn't remember writing it or thinking it, and basically had re-did the lots of work/thinking/planning/reading without any recollection of having done it before. And came to the same conclusions as well! Scary!

Yes - I am gonna have to start doing something similar to stop myself double working! And yeh, the conclusions do feel pretty robust now!

I had a similar experience on this site. I got stuck with the software I was working with and googled for solutions. It came up with a post of MINE on here, detailing how to resolve the problem! Not only had I forgotten how to solve the problem, I had forgotten even having the problem before!