- C18: Zonal Qualifiers 1998-1999
- C19: Zonal Qualifiers 2000-2001
- C20: Zonal Qualifiers 2001-2002
- C21: Zonal Qualifiers 2002-2004
The first two of these pages are lacking any sort of timestamp, and all are missing information about their original source. The third has two lists, with some discrepancies between the two. I'll try to sort these out in a separate effort.
Working backwards, the next three cycles are going to be more challenging, because I have little information about their organization. Here are links to their crosstable pages.
The C15 and C16 events were Swiss systems. The Interzonals for cycles before C15 were organized as one, two, or three separate round robin tournaments.