I’ve noticed some files I opened in a text editor have all kinds of crazy unrenderable chars
But its still contains the actual data in a faithfully reproducible/useable way?
Yes. Decoding a base64 encoded string will give you back the exact original data.
Importantly though, this isn’t what you’re seeing when you open files in a text editor as you describe in your original post, and if you copied the text of those files and saved a new copy it’s very likely that it would not reproduce correctly.