How many of the katars we know were court katars?

[Jens Nordlunde]

Yes the katar could be used for slashing - at least some of them.
Here is an early description of a katar from my catalogue A Passion for Indian weapons p. 10.

Gustav Oppert, a scholar of ancient Sanskrit manuscripts, offers a reference under the subject Amukta, a description of a weapon,
which is likely to be a katar.
“The Maustika (fist-sword, dagger) has a good hilt, is a span [circa 20-22 cm] long and ornamented. Its end is sharp, it has a high neck15, is broad in the midst and dark coloured.
It can make all sorts of movements, as it is a small and very handy weapon. Its qualities are enlarged upon by Vaisampayana”. In the above quoted text there is a footnote to a Sanskrit text, translated here. “The hilt of the Moushtika is easy to hold and gives a tight grip. Both sides of the hilt are large and with attractive designs. The tip is wide and is sharp and shining. The centre [of the blade] is thick and shining.
It can be held and circled. While turning it, number of points on it can be observed. As with the curve that cows urine makes while falling on the ground, the moushtika can also make similar curves and can be turned. It can be thrust forward and reverse, left and right, zigzag, curvy and also in a circle. It can also be thrown, turned fast and can be thrust to the ground. It can be reversed and struck to the back. We can rotate ourselves [our body] while using it. We can hit from near and hit from a
distance. It shivers, and these are the different methods of using the weapon.
This is the speciality of this weapon, O King.” This was a conversation between someone who was a master of this weapon to the king to whom he was explaining it in 2 parts; firstly its description and then on how to use it.
That the weapon “can make all sorts of movements” is an interesting observation, and the author continues to describe other weapons in a similar way – the kunta [lance] can only be handled in six ways whilst the gada [club] has twenty different motions.