Ameritech rate detail notes 
Available from http://galbithink.org/telcos/ameritech/ameritech-rates-readme.htm
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Prior to the filing in 2000, rate detail files do not explicity include crev and prev.

for 1995 and 1997 rates described as "none" set to 0

1997 through 1999 includes rate elements with "ICB" (individual case basis) reported as rate; in all case demand=0. Rate was set to 0.

1999 rate detail includes a rate-change marker and explicitly calculated change in rates.  The change marker and the rate difference are consistent with the rate data.  Both the market and the change fields were deleted in the compiled dataset.

Revenue differences: 2009 filing has 156 trunking elements with 0 crate and prate, but >0 crev and prev.  The source file gives trunking rates only to the nearest cent.  These rate elements had rates less than .005.  Seven common-line basket rate elements in filing year 2004 have calculated revenue differences with absolute value greater than $10 but less than $35.   All other revenue difference are less than $10 in absolute value.

2001, ln 110: corrected obvious error in prev entry ($2,349 => $23,489)

1999: five marketing basket elements identified and coded within common-line section

filing year placeholder lines added to dataset for missing filing years1996 and 2002