bbdb/wl-header getting any fields

My current definition of bbdb/wl-header is as follows:

(defun bbdb/wl-header (header)
  ;; (debug)
  (with-current-buffer (get-buffer wl-summary-buffer-name)
    (elmo-message-entity-field
     (elmo-message-entity wl-summary-buffer-elmo-folder
			  (wl-summary-message-number))
     (intern (downcase header)) 'string)))

When I use

(setq bbdb-auto-notes-rules
      '(("User-Agent" (".*" mailer "\\&"))))

nothing happens in my bbdb buffers.  But if I use

(setq bbdb-auto-notes-rules
      '(("From" (".*" mailer "\\&"))))

Then there is a mailer: field for everyone.  I did this test to prove
that I understood the bbdb-auto-notes-rules list.  The documetnation
there is ... beyond my understanding.  :-)

As far as I can follow the debugger step by step into the depths of
elmo-message-* and friends, I think that only a few headers are
actually "indexable" by the mail engine.  Is this the case?  I would
like to bring in a number of other fields, such as

Organizaion:
X-Spam-Level: 
X-Spam-Status:
Envelope-to:
X-ML-Name:
X-ML-Info:
User-Agent:

Thank you,
Rob