Incwage topcodes in 2004

Does anyone know why the topcodes for incwage are so much lower in 2004 compared to either earlier or later years? For example, the topcode in CA goes:
2003: $310k
2004: $215k
2005: $415k
2006: $416k
There are similar patterns in all states, with average state topcode for incwage falling from about $320k in 2003 to about $200k in 2004 and then returning to about $365k in 2005. I know topcoding changed in 2003, but what happened in 2004?

I’ve asked the IPUMS USA team about this and they weren’t aware of this pattern. It may be related to the fact that 2004 was still in the testing phase for ACS (2000-2005) so the Census Bureau was making lots of changes to the survey and editing procedures during this time. I’d recommend reaching out to the Census Bureau directly for more details.

I also found the same problem. In 2004 much more people’s incomes are top-coded.