I am not sure if these different ways could be separated by a given date or even period. I think that they existed side by side for a while. In addition to that, punching a hole (not 'chiselling') into the warm steel with a pointed TAGANE and then drifting it open to the desired width often gives better and 'cleaner' results than a hole that was drilled (cold) with an early drilling device where we see that drilling from both sides often resulted in not perfectly matching holes. Later blades may indeed show holes with sharp edges (and this may indeed allow an assessment of the age), and badly/recently made MEKUGI-ANA may even show some remaining burrs. In my opinion we have to think about the increasing habit of chiselling a MEI into the NAKAGO by the beginning of EDO JIDAI. This was done cold, while in KOTO times, punching a MEKUGI ANA was perhaps closer to the forging process and done hot while the blade was still near the anvil. From an aesthetic point of view, I like the 'old' punched and drifted MEKUGI-ANA much more, the edges of which are a bit smoothed and rounded by slight corrosion and a lot of use. Just my two YEN.