Yup, the XVII century was long, about 100 years
I just found funny that you didn't quote the part that didn't fit your argumentation, plus random passages from internet aren't really an exact source (check one wikipedia page in 2 or 3 languages: you quite often get major differences)
Polish Commonwealth is a direct translation from Rzeczpospolita Polska.
And i'd still maintain that saying that it should be renamed to a name seldom used at the time, for historical credibility is kind of paradoxical.
In my opinion it wouldn't be a bad idea for education/information purposes if it would fit, and that commonwealth or polish commonwealth are logical alternatives.