Thanks for removing it. The problem is that it wasn't always wrapped in <p> tags like your first example. Hopefully this will work better:
Code:
(<A name=\d+>\s*</a>)?\s*(<[biu][^>]*>)?\s*Generated\s+by\s+(ABC)?\s+Amber[^<]*(<a\shref=.*?processtext.*?>)?\s*(.*?processtext.*?</a>)?(</[ibu]>)?\s*(<br>\s*)?
Note the file is still going to be plenty messed up, it's been through multiple layers of munging with garbage in it - lit -> ABC pdf -> Calbre -> Calibre. You're better off trying to find a source for the original Lit.