Try it. It is part of a routine, not something that must function perfectly on its own. Anytime it does help is a win!

I would identify templates used by various sources. That is, find messages that look alike. Write code to recognize that template, and extract.

If it doesn't match that template, try to recognize the next one, and so on.

Present the text and the filled-out record to the operator. He can correct the fields, fill in the ones it didn't get, and generally have less work to do than filling out the form by hand from scratch.

Keep a new list of the ones that did not parse at all, for further investigation. Keep a list of those that needed correction, for tweeking of the parser.

I've worked that way when importing data. It didn't have to work in every case, just save me work. Pulling out the ones that worked and looking again only at what doesn't work turned out well, for identifying new patterns.

—John