It would seem we have established that the kora existed in basically the same form we see in most collected examples with the 'rondel' type hilt (simple tubular grip and disc at pommel and guard) as early as c.1560 by the example in the Nepali Museum. While that weapon seems well provenanced, I remain reserved on it as an example to set the earliest examples of this form.
The Danish examples, numbering 7 koras from 1674 and 8 by 1689, seem to offer a bit more established target in dating the form, however I found it most intriguing to determine how these most esoteric swords might have ended up in Denmark.
While the East India trading of England, Netherlands, France and Portugal were well established in India, lesser known is the activity of Denmark there. A trade factory for Denmark was established at Trankebar in 1620, which is located far south near Tanjore in Madras. The trade activity of Denmark met with considerable difficulty and conflict with Mughals and other powers trade networks. While it would seem that the location of the Danish post on the southern part of India would have little to do with the extremely northern and remote region of Nepal, there are some possibilities that might explain.
In Tamralipti in the Ganges basin, maritime trade extended south as far as Ceylon, and to SE Asia and Indonesia to the East. It seems plausible that items such as koras, might have found thier way to such trade (as Jens has noted, at least one example was used by an executioner in Ceylon). It is known that there was considerable privateering activity by the Danes from about 1640's into the 1670's in the Bay of Bengal. Possibly these weapons may have been acquired in these instances, finding their way as interesting and exotic examples back to Denmark?
Returning to the original question on the earliest date of the kora as a sword form, it seems that mid 17th century may be reliable enough as per the Danish provenanced examples, and pending more research on the Nepali Museum example we may be able to push to mid 16th century. While the focus is of course trying to find the date or period, considering the regional development and ancestry is necessary to establishing chronology of the form if possible.
I rather doubt that the kora as a form developed in Nepal without influence from other regions, much as the kukri reflects influences from the kopis with its widely diffused ancestry. It would seem likely that it did derive from the Hindu weapon forms from the Deccan via Bengal, as the early iconographic profiles suggest. I am unaware of an edged weapon that may have existed in Nepal prior to the kora that might have led to this form. Since Nepal was primarily Mongolian ethnically from early times, probably earlier edged weapons would have reflected those influences. The kukri seems to have entered the Nepali sphere via Northern India diffusion carrying the forward angled blade form associated with the ancient kopis.
The Tibetan versions of the kora, I believe are typically longer, thinner blades, although the form overall is essentially the same. In John's grouping of koras shown on this thread, he notes one of these as from Bhutan. It seems that it is incredibly difficult to discern Tibetan from Bhutanese weapons, and for purposes here they are essentially the same grouping.
In any case, I am inclined to consider that the Tibetan examples are longer and narrower as they may have been intended primarily as combat weapons, while Nepali examples are often ceremonial/sacrificial and shorter (although clearly they found occasion for combat as well, especially earlier examples).
It would seem that the kora may have developed in Tibet via tribal interaction from Nepal, and that became the northernmost extent of the form.
These are clearly my own speculations, as always pending further research
, and I look forward to corrections and opposing ideas. I know I've learned a lot from what has been posted thus far on this thread, and I'd really like to see us get further on researching these intriguing swords!
All best regards,
Jim