In respect of other wrongko forms that lack a defined angkup, whether the sans angkup form is original or is the result of remodeling.
1) Attached is the Candi Sukuh form referred to in post #9. The form from which this form is probably derived is quite similar to the form that we now know as Bugis, and can be seen in the Candi Panataran reliefs. See images.
2) Central Javanese ladrang forms that do have a defined angkup but that have lost this angkup are never original creations, a Central Javanese ladrangan without angkup is always the result of an alteration, the loss of the angkup makes the keris unsuited for formal wear & for court wear, in some non-formal settings, such as wear in a village non-formal situation it could be acceptable, often this loss of angkup has been done by a dealer in preparation for sale, if for sale to a local, in the expectation that the local buyer will redress to suit his own needs & taste, if for sale to a cultural outsider, because the cultural outsider will not not know the difference in any case.
3) The Balinese wrongko form that does have a very slight "angkup" is the Sesrengatan form, it is the direct Balinese equivalent of the Javanese ladrangan form, it is used for formal & official occasions, & the same restrictions on use for a damaged and/or modified wrongko apply in Bali as for in Jawa.
See here:-
http://www.vikingsword.com/vb/showthread.php?t=26082
4) For North Coast variations both original & modified from other forms, see here:-
https://www.vikingsword.com/vb/showthread.php?t=13435