As you research, you need to be aware of the concept of preemption. In general, a Note is preempted if a previously published work discusses your topic so completely that there’s nothing new for you to say, or if events have resolved the legal controversy you analyze. Your work should make an original and useful contribution, and preemptive authority renders it less original and less useful. Additionally, if you hope to submit your piece to a journal for publication, you should know that journals may deem a preempted piece unpublishable. Journals differ on where they draw the line between preempted and publishable Notes.
Because it is usually possible to “write around” preemptive authority, it is best to think about preemption as a matter of degree. Legal change that resolves the central legal controversy addressed by a Note is the strongest form of preemption. For example, if a Note analyzes a circuit split and the Supreme Court resolves that split, the Note may be of less interest to academics and practitioners. Similarly, a Note analyzing a statute might be preempted if the statute is amended. It can be more difficult to write around this type of preemption, so you would be wise to avoid issues that are likely to be resolved soon.
A weaker form of preemption occurs when a professor or student publishes an Article on the legal issue you are researching. Although you certainly do not want to have to cite another source for the central proposition of your Note, you should be able to shift your focus or tweak your thesis to keep your Note original and useful. Finding an existing Article or Note on your topic can even be a blessing—you can mine its footnotes for sources that you may have overlooked, and it may raise unanswered questions that you can address or call for further research that you can supply.
---Language from https://www.law.nyu.edu/students/studentwriting/preemption
Preemption checking is the process of surveying the existing literature to make sure that the topic you have chosen for your note or comment has not already been covered by another author. Be aware that preemptive material can appear in a wide variety of sources, e.g.:
Therefore, you should be as comprehensive as possible in your search for potentially preemptive material. Begin with the legal literature, but also look for book chapters and articles in other disciplines, as well as theses, dissertations, working papers or conference papers that may be on their way to publication.
This guide is intended as a brief introduction to resources for preemption checking when preparing a journal note or comment. For additional help with preemption checking, consult one of Rodino's Reference Librarians.
When looking for law review articles on your topic, you may find it more productive to search by subject in a journal index, rather than by keyword in full-text resources like Westlaw, Lexis+, or HeinOnline. Subject searching eliminates many irrelevant search results by pointing you only to those articles that are primarily about your topic instead of mentioning your search term anywhere in the article. Most articles will then be available by clicking on the “PennText” button next to the citation, or you can find the journal by title through LOLA or Franklin and then locate the article of interest online or in print.
If searching by subject in a journal index doesn't return any preemptive citations, move on to a keyword search in a full-text source.
Just as the law review indexes suggested above make searching for legal literature more efficient, indexes in law-related disciplines make it easier to search for articles in journals of international relations, business, religious studies, medicine, etc. A few frequently-used indexes are suggested here, but to find additional indexes for the field(s) relevant to your subject, check Van Pelt Library's lists of e-resources by discipline.
Library catalogs frequently include table of contents information, allowing you to search not only for books about your topic, but also individual book chapters. In addition, resources such as Google Books allow you to search even deeper within a book for sections about your subject.
Works that have not yet been published, such as working papers or papers presented at conferences, as well as those presented in completion of a Masters or PhD degree, can still be preemptive. Be sure to confirm that no one is currently working on your topic, and may have published by the time your note is ready to submit, by checking the resources below.