Quoting Thomas Klausner <wiz@netbsd.org>:

> mdoc hackers to improve .Nm are welcome, I can supply more details
> or a test file.

not an mdoc hacker, but with the patch below, an empty first argument to 
the .Nm macro gets replaced by the command-name.  AFAICT this "fixes" the 
compatibility issue.

--- tmac/doc.tmac.orig  Fri Jul  5 16:37:21 2002
+++ tmac/doc.tmac
@@ -906,8 +906,16 @@
 .de Nm
 .  if !\n[doc-arg-limit] \{\
 .    ds doc-macro-name Nm
-.    ie \n[.$] \
+.    ie \n[.$] \{\
 .      doc-parse-args \$@
+.      nr doc-arg-ptr +1
+.      if "\*[doc-arg\n[doc-arg-ptr]]"" \
+.        ie "\*[doc-command-name]"" \
+.          tm Usage: .Nm name ... (#\n[.c])
+.        el \
+.          ds doc-arg\n[doc-arg-ptr] \*[doc-command-name]
+.      nr doc-arg-ptr -1
+.    \}
 .    el \{\
 .      ie "\*[doc-command-name]"" \
 .        tm Usage: .Nm name ... (#\n[.c])

-- 
Christian Limpach <chris@pin.lu>