From the start of the mission until December 2002, the rear decimation information was not available in the data stream. 

From the start of the mission, until July 11, 2002, rear decimation usually, but not always, occurred at S/C night at high latitude.

From July 11, 2002 until December 13, 2002 rear decimation occurred during both day and night.  (Browser quicklook 'Corrected' plots were able to correct for decimation during this period even though the decimation information was not in the data stream, by using the high-latitude flag which was available.)

For 2002 through mid-December, these are the changes made in the rear decimation state (see the RHESSI Decimation/Event Download Status Record for the full list of changes for 2002-2005, and more explanation of the codes).
D = Day
N = Night
H = High latitude
O = Off
r = resets off
B = number of minutes before and after day for fronts to be on
Number = rear decimation setting

2002    02    17    22    30    r,93
2002    02    19    19    20    r
2002    03    ??    ??    ??    D:r N:r,93
2002    03    30    05    00    r
2002    05    03    05    00     D:r [N+H]:r,83 B:2,2
2002    06    13    00    00     D:r N:O B:2,2
2002    06    14    00    00     D:r H:r,83 B:2,2
2002    06    25    00    00     D:r [N+H]:r,83 B:2,2
2002    06    27    00    00     D:r N:r,83 B:2,2
2002    07    11    00    00     D:r H:r,83 B:2,2

So from February 17 until sometime in March, the rear decimation level was 93 (93 means 3/4 decimation for channels less than 9*128 or 1152). In March, rear decimation was set to happen only at night. On March 30 , no rear decimation. On May 3, rear decimation was 83 (83 means 3/4 decimation below channel 1023) at night and high latitudes.  Decimation is turned off on June 13, back on the next day, for day and night, reset to N+H  on the 25th, and back on for both day and night for the 27th. There are no changes in the table until December 2002, but by then there is rear decimation status information in the packets.