Unfortunately, the later starting dates are (ironically) out of date.
Several of them are completely broken and can be exploited in weird ways (like the Venice HRE shenanigans and the Ottomans getting free cores on the Hijaz), while most of them are not up to date in regards to DLC's and patches. (Such as Korea starting off as a vassal instead of a tributary of Qing in later dates).
Updating the later starting dates would most likely require a large amount of dedicated time and manpower, and is unlikely to happen this late into the game's life-cycle. Hopefully EUV, whenever it comes out, will have fewer, but better made starting dates so that they aren't abandoned like in EUIV.