Is not redesigning an entire website at once bad for UX?

I have a website that I recently updated. I redesigned most of the website, but there's still some pages and features that are "old." Will this be a bad experience for users when they navigate to a page that hasn't been updated, and they see a different older design?

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I noticed this on Google's products and services, too. Many of their products and services have been updated to their new Material Design, but some other pages still have their old look.

This was kind of annoying to me, as their updated pages now save automatically but the old ones didn't. One time, my YouTube settings weren't saved because I was expecting them to save automatically like the new settings pages do.