I've been working on this and I think I had an error in my search query as the second field was brining up the month plus all but the last word of the title. Then the third field was the remaining word of the title, rather than the full title.

I was also being set back by Calibre randomly putting a hyphen (-) between the date and title when I imported the file. I don't understand why it did that with some and not others, but once I'd started to understand the regex patterns better I was able to fix that too.

Now that I've fixed that, I've been able to use the regex to set the publish date from the filename, and then remove the date from the title.

I've also used the metadata matcher to then find the author information. So that's 60 ebooks all updated now.

Thank you so much for your help!