User blog comment:Hayashi H/Advanced Equipment Guide/@comment-24930367-20151028172016/@comment-26486243-20151028185511

Rather than being wrong, it may be the case the mechanic itself was changed. Wurfgerat used to deal less damage than it does now; it's not inconceivable that they may have patched it to allow only single attacks when they increased its firepower as a form of balance.

The only thing I can say is that the last time I used it (E4 Summer 2015) with Ushio (12.7bk2 x2 + Wurf) it definitely did only single attacks, even though it should theoretically have allowed for double attacks, so for at the moment at least, it only allows for one hit.

There used to be a time in the past when using 2x 12.7cm Twin Gun Mount (Late Model) primaries would allow destroyers to do double ASW attacks in yasen nodes - and people used that property to pair these guns together with a single T3 Sonar, but it was patched not long after knowledge about it became widespread. So there is a precedent for there being double special attacks that later gets patched to become single attack-only.

I'd consider the chance of this being the situation to be higher than your memory being wrong, since things that directly affect build viability this much tend to remain in memory.