For some reason die chips that cause protrusions or blobs to appear on struck coins were unusually common on U.S. coins of most denominations struck during the 1950s and early 1960s. These chips often clogged letters and numerals and, as I recall, were the stated reason for the 1960 small date cent being replaced with the large date version.  A number of these chips also formed between the "B" and "E" of Lincoln cents, creating the impression of a letter "I".  These became known as "BIE" or "LIB