Broken/Damaged Type in Overprints. 
Overprinting is a useful and quick means of altering stamps due to changes in rates, or in this case, change of governments. In 1922, British stamps were overprinted on two occasions, first to acknowledge the Provisional Government of Ireland (Rialtas Sealdac na h’Éireann) in February, and again in November to identify the creation of the Free State of Ireland (Saorstát Éireann).
The plates with the overprint information for the Dollard printings were made from metal stereos. These were made by the use of a relatively low melting point metal alloy, which is softer than steel and vulnerable to stress cracks. In additions, some flaws came from the original type used to make the stereos.
The resultant breaks, missing letters, and spacing problems are repeatable and platable, and have been studied extensively. Here are a few examples to whet your interest. Stamps in Figures 1 through 3 show damage to the stereos while 4 shows misalignment..
Figures 1 and 1A has a missing stem of the “h” in h’Éireann on the left stamp.
Figures 2 and 2A has lost the descendor in the “9” in “1922”, making it read “1o22”.
Figure 3 provides an overall view, 3A show the damaged “h” while 3B shows damage to the “R” crossbar.
Figures 4 has the entire overprint shifted downward about 6mm causing half of the 1922 to appear on the next row, while the bottom half from the preceding row is now on the top. This was most likely caused by the sheet of gummed and perforated British stamps feeding incorrectly, thus the overprint is offset.
These are only a few of the errors or problems that have been identified on the early stamps of all values which were in use until superceded by the First Definitive series. The reference to Meredith provides a good starting point for research..
The Postage Stamps of Ireland, Meredith,W., revised by Foley, J., The Revealer, #130 and 131,April & July 1978.
Identification of the Rialtas and Saorstát Overprints, Foley, J, The Eire Philatelic Association
Fundamentals of Philately, Williams, L.N., American Philatelic Society, Revised Edition 1990, Chapter 12, p.435 ff.
“Low Value Irish Overprints – Plates and Varieties”, Priestly, M.H., D.F. Newsletter, David Feldman, Ltd, Dublin, Volume 2, #10, Spring 1973.
“1922 Irish Overprints – The Low Values”, Priestly, M.H., The Revealer, #169, Winter 1987.
The Revealer, approximately 60 articles on various aspects of the Overprints.,