Hello Jean & Alan,
I was mulling over exactly the same apparent discrepancy!
Of course, the drawing are based on specimens which have been exposed to humid tropical climate and regular cleaning & etching - so we have to allow for quite a bit of erosion when comparing contemporary Jawa features with early collected museum pieces. A ron dha nunut is crafted from relatively thin metal and, thus, more prone to change from erosion and revision. However, the ron dha is usually crafted from fairly substantial metal and I have a hard time to fathom how the base could converge into the typical form unless by the helping hand of someone eager to implement change... (The tips and hooks are much more likely to degrade during routine maintenance, of course.)
In the mean time, SÚverin posted a separate thread for this keris - maybe we can keep this thread for discussing Cirebon/North coast hilts and move the keris discussion over here?