Originally Posted by
ckpeter
Don't forgot that UA miles (with some exception that is not likely applicable to you) can be used for US and CO flights under their own saver/lowest mileage lower. So, you can use US and CO to check on awards, and then use united.com or call UA to book.
Most (all?) programs make more seats available to their own members than they export to StarNet. So searching for CO flights on CO does not necessarily mean they will be available to any partner for booking.