If we already had problems to find really accurate and detailed information about the Regnum Noricum before the Roman takeover, it is even more complicated with their only king mentioned by name, Voccio.
The very term king is such a thing. Caesar refers to him as Rex, but whether the Noricans also titled their leader as king or whether this being king has anything to do with our ideas of a king or more with an Indian chief, we do not know.
If we consult the Internet (it knows everything, doesn't it?) we find that Voccio died in 16 BC, was king of the 13 Celtic tribes, married his sister to the Suebi prince Ariovist and supported Caesar in the civil war with 300 horsemen after defeating the invading Dacians in 50 BC and then the invading Boians in 40 BC
That does sound quite useable. The only catch is that there is a connection with the name Voccio for only one of these deeds. If you guess the glorious battles, you are unfortunately wrong.
The only mention of the name Voccio is to be found in Caesars report De Bello Gallico, in connection with the Suebi prince Ariovist, whose one wife was of Norse descent, the sister of King Voccio, who sent her to Gaul to join Ariovist. (The marriage, by the way, was not very long-lasting, that said wife died in 58 BC after the defeat of Ariovist on the run from Caesar's troops. Which is probably the only reason Caesar mentions it at all).
Everything else? Speculation, simplification, conflation of facts floating in space ....
Neither do we know whether the Noric empire in Voccio's time still consisted of the 13 tribes that had united around 200 BC, nor whether Voccio was still in power (and how large was the empire he ruled) when Caesar went to civil war, the Dacians and the Boians invaded, or whether he was actually still alive in 16 BC. Especially the date of death seems to be pulled out of thin air, if one sees Voccio as an active warlord, who was probably already a grown man when he sent his sister to Gaul before 58 BC. It is likely that someone simply assumed that the Romans took advantage of the death of the Noric ruler to finally incorporate this rich territory into their empire (would not have been the first time that they used the vacuum after a ruler's death for themselves). And since the only known Noric king is Voccio, well, then it was he who died in 16 BC....
Nonetheless, I have included Voccio with all the improbabilities in my books as well. First, until recently I took what I found about him on the Internet as historical fact (I thank Raimund Karl, Viennese Celtologist at Bangor University in Wales, for clarification! ) and secondly, I already have him as the Noric ruler who supports Caesar in the civil war in my "The Bow of Smertrios", so he remains that in the new series ... (and it is not proven that it was NOT him who both sent his sister to Gaul in 58 BC and was still in power 9 years later).
I would love to be able to undertake a time travel and look like a little mouse in Voccio's hall whether the historical Voccio has even the slightest similarities with my Voccio ... and also to find out where this hall was actually located. Whether I and Günter Singer, who have chosen Deutschlandsberg for it completely independently of each other, are perhaps even right ...