For some curious reason, there are 48 observations where the CITY is preceded by the text string 'ZZ'. There are cases where CITY was misspelled but only one other case I can recall where extraneous characters were inserted before a city name. The PLDF3 schedule of changes for Nebraska documents three cases where the LIBID was also preceded by 'ZZ'. These cases were only discovered as a result of investigating duplicate entries. It seems unlikely the ZZ's are random but a quick investigation did not turn up any explanation. Here they are, in order by state:
1992 AZ ZZPhoenix
1992 AZ ZZFlorence
1992 DE ZZGeorgetown
1994 FL ZZClearwater
1995 FL ZZClearwater
1996 IN ZZIndianapolis
1992 LA ZZBaton Rouge
1993 LA ZZBaton Rouge
1994 LA ZZBaton Rouge
1995 LA ZZBaton Rouge
1992 MD ZZCUMBERLAND
1992 MD ZZBALTIMORE
1992 MD ZZSALISBURY
1997 ME ZZPortland
1997 ME ZZSouth Portland
1998 ME ZZSOUTH PORTLAND
1994 MI ZZAnn Arbor
1994 MI ZZAlmont
1994 MI ZZWayne
1995 MN ZZWORTHINGTON
1997 MN ZZROCHESTER
1996 MO ZZJefferson City
1996 NE ZZNiobrara
1997 NE ZZNiobrara
1990 NH ZZCanaan
1993 NH ZZNewport
1994 NH ZZDurham
1992 NJ ZZBound Brook
1993 NJ ZZBound Brook
1989 PA ZZBUTLER
1990 PA ZZCARLISLE
1992 PA ZZBUTLER
1994 PA ZZBELLEFONTE
1995 PA ZZMONESSEN
1996 PA ZZMONESSEN
1996 PA ZZBELLEFONTE
1997 PA ZZBELLEFONTE
1997 RI ZZCoventry
1992 TN ZZHALLS
1992 TN ZZCLARKSVILLE
1992 TN ZZNASHVILLE
1992 TX ZZGalveston
1992 TX ZZAustin
1992 TX ZZKenedy
1992 TX ZZBoerne
1993 TX ZZDallas
1993 TX ZZAmarillo
1996 TX ZZWoodville
Here are the number of these cases by state:
AZ 2
DE 1
FL 2
IN 1
LA 4
MD 3
ME 3
MI 3
MN 2
MO 1
NE 2
NH 3
NJ 2
PA 8
RI 1
TN 3
TX 7
And by year:
1989 1
1990 2
1992 16
1993 5
1994 7
1995 4
1996 6
1997 6
1998 1