Booklets With Position Marked. 
The 1983 booklet of the Four Courts (Figure 1) was the first booklet designed for use with dispensing machines. It has an unusual feature. It is possible to identify the position of each stamp in any booklet of the set to a specific position on the printing plate.
The plate layout (Figure 2) is unique in that each vertical column is identified in the selvadge by a series of dots in the selvadge column where the binding occurs. A number of dots are printed – one dot for booklets 1-10, two dots for 11-20, three dots for 21 to 30, and four dots for 31 to 40. (Figure 3) The rear booklet cover is also numbered from 1 to 40 in the lower right. (Figure 4) When assembled, the large sheet of booklets would then be cut and heat sealed together. Thus, the three dots on the booklet pane indicate this is from booklet 21. (Figure 5)
Problems arose when after the cutting process and before or during the heating to secure the booklets together, some booklets parts became loose. In putting them back together, errors were made. Thus, examples can be found with dots not corresponding to the position number.
Why was this done to begin with? Apparently to sell booklets to collectors! While interesting philatelically, it was not a selling point at a price of IRL£40 (about $45) for the full set . Had there been a major error, such as a few inverted sheets, demand would certainly have increased. But, alas, the keen eyes of quality control prevented such an event.