Back to sweet versus dry. The nihonshu-do is far from being the only factor affecting the impression of sweet or dry. In particular, acidity plays a huge role in our sensations. Sake with higher acidity will generally taste drier than it actually may be based on the numbers alone. The other side of the coin is that a sake with lower than usual levels of acid can taste a tad sweeter than their nihonshu-do would indicate.
Temperature is another contributing factor.
In my humble opinion, sweetness and dryness in sake is much more temperature-dependent than in wine, if only by virtue of sake's narrow bandwidth of overall flavor. Just a few degrees of change can make a sake seem sweeter or drier. Accompanying food has a say in the formula, as does whether or not you are tasting other sake, and if so the flavor of the previous sake comes into play. In the end, sweet or dry is a precariously subjective assessment, and nihonshu-do is at best a ballpark indication of this parameter. This is refreshingly simple after the last one.