How to preempt plagiarism accusations In 2006, when I was still in grad school, I wrote a paper that went through the usual motions: I discussed it with my advisor, I presented it at a peer-reviewed conference, and then published it as a refereed chapter in an edited volume. Right before the volume came out, I was explaining the paper to a friend from another university and he went: "oh, I think Professor Bigshot said something similar in his semi-obscure 1970 dissertation!". I checked the dissertation in question and, indeed, what I wrote is essentially what Professor Bigshot wrote in 1970, give or take some minor variations in the formalism.

Something to keep in mind here is that this is not plagiarism. I came up with the idea totally on my own, and I didn't reference Professor Bigshot's dissertation because nobody (not my supervisor, not the conference audience, not the chapter referees) told me about it in time. What worries me is that other people might think I took the relevant dissertation passage and plagiarized it. So far, nobody has happened, but I'm want to preempt plagiarism claims in the future. Obviously, nothing can be done about the published chapter, so I have modified the downloadable preprints in both my website and the go-to repository of my field, adding a note that explains the situation and giving proper credit to Professor Bigshot.

Is this enough, or is there anything else I can do?
It is hard, if not impossible, to pre-empt accusations of plagiarism. The key is to be prepared to defend yourself. People rediscover stuff all the time. I would make sure that you keep all of your notes, drafts and any literature searches you may have done. I think keeping them privately would be fine, but if you really wanted to, you could make them publicly available in an archival manner to demonstrate that it is really your work.