In an earlier article on finding certain issues of Korea, it was mentioned that this author has been searching for a Korea 1956 Scott 212E on horizontal laid paper for many years. See Figure 1 for an example of 212E on vertical paper. The Scott catalogue makes a note under 212D-F, that all three exist on horizontal paper.
Mostly likely the majority of Korean collectors do not distinguish between the vertically laid paper and horizontally laid paper varieties. When looking at the backs of the laid paper one can see faint black lines that go either in a vertical or horizontal direction. See Figures 2 and 3 for examples of Scott 235 and 236 on both horizontal and vertical laid paper. Some of the commemorative issues such as The Rhee Monument, Scott 226 were also printed on both horizontal and vertical laid paper. See Figure 4.
Robert Jones wrote an excellent article for the Korean Philatelic in May, 1973 Vol XXIII, No. 2 about the laid paper printing process and which individual issues had the vertical and horizontal printing. It is well worth reading the article (see figure 5 at the end of this text).