Redirect errors in webmaster tools after permalink change [multisite]

Hello,

I’ve racked my brain trying to solve this problem and I’m finally in need of help from some experts. Allow me to give you the required information:

My website: https://clubpenguinplanet.com

My .htaccess: https://pastebin.com/KpU2iFNp

The issue: Google webmaster tools is finding over 1000 new 404’s on my site daily. It’s currently at 5,183. I know the 404 errors are a result of a change in permalinks that I made, and that WordPress is not automatically 301 redirecting them (probably because I have too much content on my blog).

Here’s a rundown of what I did to cause this issue:

I’m running a multisite installation. I’m using subdomains, so I was able to change the default permalink structure for multisite (/blog/%year%/%month%/%day%/%postname%) to (/%year%/%month%/%postname%). Just before getting the idea to change this permalink structure, however,I uploaded XML backups of posts that I’ve made since 2007, importing nearly 1000 posts, hundreds of thousands of comments, and tons of tags. It was a silly mistake on my part to not have changed the permalink structure before uploading the backups.

However, this is where I’m at. I imported tons of content using the “/blog/*/” permalink structure, and after changing the structure not everything redirects as intended. Here is a quick screencap of some of the pages that are returning 404.

https://prntscr.com/3sll60

As you can see, the 404 is coming from tag pages (I used a lot of tags back in the day). If you remove the “/blog” from any of those tags, the page loads correctly. How can I modify my .htaccess (or otherwise) in order to allow any page with /blog/ in front of it to redirect to the correct format?

Thank you, your help is much appreciated.
Adam

P.S. The site functions fine and all of the pages load properly, the issue is that some pages, when visited using the old permalink structure, return a 404 instead of redirecting to the new permalink structure.