I know absolutely nothing about kudi, but thought since these fields of weapons are the primary focus here it would be fun to learn something. Basically just using our search feature I read some notes provided by Krockew (2 Dec 2007 and illustration attached) where he explains that the three holes are typically associated with the older Hindu examples. The later examples with five holes are believed to represent the Five Pillars of Islam.
It seems that pierced holes in blades are well known in a number of different cases in various cultural spheres and regions, but no definitive explanation has as yet been proven that I am aware of. Naturally, I always hope someone might step forward with such information, but......
I will simply add some information on strategically placed holes in blades for entertainment. The parang ihlang (mandau) of Borneo blades typically have pierced holes along the back of the blade, and occasionally a number of these are filled with copper. The obvious but unproven (as far as I know) suggestion that these are 'tally' records in headhunting would clearly have nothing to do with these kudi blades, just an interesting note.
In India many blades on so called temple swords are lined with holes in linear fashion along back of blade presumably for auspicious festoons in the ceremonial or ritual use, and similarly placed holes are found in many Chinese swords.
Since these holes in the kudi blades seem to align with blade profile perhaps they are simply openwork to enhance the dimensional appearance of the blade itself? and while the holes themselves have no practical use, the numeric symbolism of the features have perhaps such meaning. The number three is of course a key number in Hindu theology as well as Buddhist in the Trimurti) . Unrelated it is paralleled in the Christian trinity.
As always, the more pragmatic will suggest simple aesthetics.
Hopefully the thread will move beyond this post and the experts will offer more plausible suggestions or evidence.