Any throw that lands a person largely on their back, with force and control, without entanglement (locking out of the knee) of the legs, is valid for Ippon.
Anything less, they give you points, but allow groundwork to proceed. This was a freestyle judo ruleset, so they allow groundwork without stalling, you stall, or get stuck in a position because the other guy is stalling, you get stood back up. IJF Olympic rules give you about 10-20 seconds to obtain a submission before they stand you up.