Shouldn't the assumption here be not that the taboo didn't work, but that Voldemort was powerless to respond to it when it was triggered? Like, he was a disembodied ghost in the ass end of Romania; he wasn't going to be able to show up and wreck anyone's day if the taboo alerted him to it.

 

Also, that random beam Harry did was a result of his wand learning Voldemort's spells or something from GoF, right?

Regarding the taboo, it seems like something that requires Voldemort to take over the ministry to do, which didn't happen in the first war. I think for the first war, he simply used rumours and his spies to terrorize people who seemed to stand against him. It was only in the second war that he could use magic to enhance to his effectiveness.