I'm not sure if APO actually means anything specific design-wise. I could be wrong, but from what I'm gathering it's more of a characteristic. APOs tend to use triplets to get to an apochromatic quality, but there isn't really an APO "design" per-sey, and any number of designs could be considered apochromatic so long as it roughly follows an apochromatic dispersion curve, or, perhaps not as there's no saying what lens manufacturers might consider "apochromatic".
I was kind of surprised by this, and I always assumed APO actually meant something generally specific, like "Double Gauss", "Tessar" and "Petzval".