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