Client copied all blogs from old site and posted them verbatim on new site - leaving the old content still in place. Do I make new pages for updated content (on new website) or just add the new content to the already existing pages (deleting copied content) that currently have copied text?

This is the first time I've run into this. Client took all content from Site A and put on Site B. Site A content is still up. I know this can't be good for SEO - especially since it's hundreds of blogs.

I'm rewriting the content so Google doesn't think it's copied from another website. With this new content for Site B, though, should I make all new pages and delete the pages with that have copied content from Site A?

I'm wondering if those pages with the copied text may be flagged on Google (some don't even show up on Google when I search text verbatim directed at the site specifically). If so, it seems making new pages may be ideal.