Tacitus and Pliny were writing four hundred years after the start of your mod. A lot can happen in four hundred years. I agree that Norway and Sweden were "Civs," but in 100 A.D., not in 300 B.C.E.
The south Scandinavians spoke a language called Proto-Norse (also called Proto North Germanic and Ancient Nordic) which in turn became Old Norse which was, as I recall, the immediate pre-cursor language of Norwegian, Swedish, Danish, Frisian, and several others.
Finno-ugric is also a language and is one of the few descriptors we have for the people who moved out of the area of Estonia into Hungary in the south and Finland in the north. Some of those early Finns continued to move into northern Sweden and later northern Norway.
DNA confirms these patterns. Norse DNA consists of three distinct Y (paternal) DNA haplogroups: I1, R1b, and R1a. The vast majority of the inhabitants of Iceland, Norway, Denmark, Sweden, Northwest Germany, and the Western Islands of Scotland belong to one of these three groups.
With regards to Finns, 60% belong to N1(=Estonians) and around 40% belong to R1a or R1b. N1 is also found in the more northern populations of Norway and Sweden.
The generally held view is that Northern Scandinavia was settled (or "civilized") much later than Southern Scandinavia. Shift your timeline slider back and you have fewer civs; shift it forward and you have more.
Fortunately for game designers (or unfortunately) depending on your point of view, we know very little about bronze age Scandinavia. Historical references are scant, names given to its peoples and geographic regions are obscure, and the physical record they left behind (e.g. burial artifacts) are meager. So..., consider your design restricted by what you know or liberated by what you don't know.
On a final note, I much prefer Gaius Plinius to Publius Tacitus. Tacitus owed too much (as he admitted) to his Flavian sponsors to be completely objective in his writings.