There is a type of gayaman wrongko which is attributed to Tegal that has each end of the gambar dipping down, instead of flat or up.
Do you know of any examples of this type which exhibit the "double lip" Paul pointed to?
This "double lip" seems to be a feature restricted to the other North coast scabbard type AFAIK. It is an even more common (though by no means universal) feature of early collected (Kunstkammer) scabbards and, thus, very likely to have very old roots.
A gandar that has its top section with kruwingan and its bottom section with no kruwingan and no ada-ada is common in Bali keris.
There are also quite some traditional scabbards attributed to Cirebon which display this feature. I wonder whether this may also have old roots popping up in different extant cultural contexts (and, thus, making it difficult to use it to narrow down the origin of Paul's variant scabbard)?