Re: When is koshinage not koshinage?
Peter (et al) - The "T- formation" style of koshinage is rather unique to aikido, I believe. Most wrestling systems worldwide use the "parallel hips." (I cannot speak to Daito-ryu - I don't know how they do it). Given that the oldest photos and films of Ueshiba M. show him doing the T-style, I believe that subsequently, shihan with judo experience imported the parallel style that is, as you say, more adaptable. The T-style is almost purely a timing throw, and gives far less room for error. Speaking as an individual of 2 meters in height, I'm well-aware that if I'm not low enough (which I haven't been for years), I cannot bring off the either throw unless my uke is compliant. Were koshinage required, either in practice or as a teacher, I might find myself doing one of several errors: too high on the back, straightening the knees to lift uke up, too much power in the arms thereby trying to lift them with brute force or, legs too widespread - all of which make the technique easily neutralized with a non-compliant uke.
One of the most beautiful examples of koshinage as a timing throw is a film from the 50's or 60's of Tohei K., in a multiple attack sequence.
Ganseki-otoshi is, I believe, a "show-waza," derived from Daito-ryu. Grabbing the back collar and stepping through with a leg-sweep, or a simple body slam is the actual technique. Ganseki-otoshi is, biomechanically, not so strong. That's why, I believe, you do not see it in any competition grappling system (sumo, Mongolian wrestling, European, etc.). In my opinion, it's more like a Pro-wrestling waza which would be devastating, but requires that uke allows the other person to hoist or lock up.
Finally, Koroiwa Yoshio had an utterly unique koshinage, which has to be seen to be believed - derived from a western wrestling single leg entry, sort of like a kata-guruma, except uke goes from shoulder to opposite hip. He is famous in the Asakusa-bashi neighborhood when he dispatched a amateur sumo 4th dan, yakuza with several successive throws of this kind when the latter was busting up a friend of Kuroiwa's dojo.