I have a specific short Holland question:
Utrecht annexed Gelre early on in the game, while I was still under a PU with Hainaut (For some eason, Burgundy put Hainaut in their sphere of influence, and didn't attack. I had to wait for the ruler to die, before I was free to pursue my own wars). Soon after, England was involved in 5 different wars at once, including one with Utrecht and it's allies. So I took the chance, and vassalised Utrecht when I asked England for an Alliance. But Gelre was attached. Now, I can't seem to get the 'incorporate Utrecht into your country' mission. Is this because of the fact that Utrecht still holds Gelre, as my vassal? In effect, can't the mission fire because Gelre would be a part of the bargain as well?
I just aggro vassalised Friesland, and got the mission to incorporate it like, one mission later...
If you are playing the beta this might be the case. I'm not sure about 5.1 but I know there were, at one point, complaints about getting the incorporate mission and ending up with unlawful territory because of it so that may have been addressed in a patch.
If you haven't expanded elsewhere it is because they have as many provinces as you. This definitely blocks the annex vassal mission.