From the latest SC3:

b. Triangle Speed Course as in 3.1.5g with distances of 100, 300, 500, 750, 1250 km, or greater multiples of 500 km. A record may be claimed for the declared course and any shorter triangle in compliance with the applicable triangle geometry requirements in 3.1.8.

They skip 1000, 1500, 2000, etc...

5Z