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What are some of your favorite sites that guide updating a ~4 year-old CV?
The HR Digest, The Muse, and Balance Careers are a few leading websites that give insights related to Resume/CV writing.
Willing to have a look over for free if you'd like.
https://owl.purdue.edu/owl/job_search_writing/resumes_and_vitas/writing_the_cv.html
I think Purdue OWL does a good job talking about CV and writing one. They also list a few other resources at the bottom as well.