Update: I wrote back and asked for clarification as the phone response was exactly opposite the first written response.

I got a reply that was a lot more strongly worded in ANZ's favor, but didn't actually cite anything in Airpoints T&C. They seem to treat it as a Roll Over case, which I don't exactly agree with, and they don't seem too interested in doing anything about it. They did reiterate their offer of "call us if you only need 5SP to upgrade and we'll see what we can do," but I imagine that only applies if it's a very small number of SP you need (<10?), and that just seems mired in gray area.

I consider it pretty rotten to say "this flight will earn you 400SP" and then find out that 375SP will vanish forever because you only needed 25SP to make Elite. Altruistically, I still disagree with their policy (or apparent lack thereof)! I guess they've adequately performed CYA by saying "potential SP earning."

For my situation, a couple segments on United in the US earned more SP than I expected, and I got a cheap long haul Y-J upgrade that carried lots of SP with it, so I ended up making Elite sooner than expected with "only" ~40SP going to waste. And of course, now that I'm Elite, this theoretically won't happen again as I'm in the land of Elite Roll Over and not traversing status tiers any longer.