I was able to book two seats for friends IAH-SYD in C class during February (during America's Cup time and Sydney Mardi Gras); no problem when I changed them to April. (Except I was unable to get FC on the IAH-LAX and SFO-IAH legs.)
FWIW, I was able to get a BC seat on Qantas LAX-SYD during February, and FC in April using CO OnePass miles.