Another S. Korea-coin enthusiast and myself are trying to figure out what explains the lower relief on the "7" in the date on some examples of 1970-era 100 Won coins (KM-9): 1973: 1974: There are many in the 1973 and 1974 dates that exhibit this "soft seven" but not all of the coins that you find in this date range have the "soft seven." Some possible culprits could be wear (which I doubt), or struck through grease (or something). My own thinking on this, with no information from Korean sources to further explain this phenomenon, is that these coins were not fully struck, since the relief on the "date" side of the coin did NOT avoid an extreme area of relief on the opposite side (Admiral Yi's left eye). The area of the void where the planchet metal must flow between the dies was too large, and the planchet was insufficiently constrained when struck, the pressure in the metal dropped, and the metal did not fill in the recesses of the dies where the most metal is required. On the date side, that happened to be right where the "7" was. The weakness also seems to affect the numerals "9" and "4" (or "3") in the areas of those numerals closest to the "7". So, perhaps it was insufficient striking pressure, or design flaw, or both. Any other possible causes?
Given what I can see, and what you report, I'd have to go with both. But to firm that opinion up, let me ask you - on the coins that have the weak 7, is the band on the hat also weak like it shows in the picture ? If it is, then I'd be reasonably certain that that "both" is a correct analysis. That said, since you mention that not all coins of these dates have that weak 7, it would seem that increased strike pressure is capable of overcoming the design flaw.
The area of the hat band on these coins is generally weaker in all of these 1973 and 1974 dates with the weak seven, and without it. This is based on decent images of about 40 different examples, as well as about 20 different in-hand examples. The hat-band area is also the first area to wear on circulated examples.
