Merging a decade-old site with Grav?

So I'm working on a site for a music festival that's been going since 2001. Each year of the festival has been a different folder on the server. There hasn't ever been a CMS for it, every year has just been files in a new folder for the given year. So the URLs have been fest.org/year01, fest.org/year02, with fest.org redirecting to the most recent year (fest.org/year16 in this case).

Since it's just files in folders, Grav seems like a good replacement for future years of the festival, but I'm worried about how routing is going to work against all these old folders. I'm assuming that once I'm done, I need to plant the whole Grav folder in the server's webroot, which will set up a lot of its own routing. But won't that override the routes for the still-present folders in /year01, /year02, etc? Any recommendations for routing overrides? I briefly considered porting all the old years to Grav, but the old ones are way old, design-wise - like, table-based layouts with pictures for text.

You can simply put your physical folders in the Grav root folder, and they will take precedence over Grav's own routing.

If you then want to integrate it a bit more, you could start by making a user/pages/year01/year01.md, and copy the old HTML into user/themes/yourtheme/templates/year01.html.twig, then convert the referenced CSS/JS file paths, and so on. Here's a tutorial of how I moved an HTML theme to a Grav theme, if this can help: http://gravcart.com/blog/create-a-grav-site-theme