Improve the existing note before creating another copy
Finding a second explanation of the same idea does not always require a second note. If the new source adds a clearer example or an important qualification, update the existing explanation. One maintained note is easier to trust than several overlapping versions that disagree silently.
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Consolidate what answers the same question
You already have a note explaining a process. A new article describes the same process more clearly and adds one useful exception.
Creating a second note may leave two competing explanations that need separate maintenance. Updating the existing note can preserve a single useful answer. Add the better example, include the qualification and retain the relevant source details.
Separate notes still make sense when they answer different questions or offer genuinely different applications. Similar vocabulary alone is not enough reason to merge them.
The test is whether a future reader would need to compare the notes to reconstruct one complete explanation. If so, consolidation may remove avoidable work while keeping the useful distinctions inside the revised version.