While the PKK has been designated as a Foreign Terrorist Organization by the United States, the United States' position on the YPG is that it is not a terrorist organization, a stance that has generated much conflict between the two NATO allies. Despite this, the CIA named the PYD as the "Syrian wing" of the PKK in its World Factbook on 23 January 2018. On 14 February, Director of National Intelligence described YPG as the Syrian wing of PKK in its new report.
PYD is one of the [if not the main] political organization[s] running the YPG.
In mid-2012 the People's Council of Western Kurdistan signed an agreement with the Kurdish National Council (KNC), forming a joint Kurdish Supreme Council (Kurdish Supreme Committee) and agreeing to cooperate on security for Kurdish areas, forming People's Protection Units (YPG)
So it is a bit strange how the Kurdish politicians are terrorists in CIA's view, but their YPG troops are not.
Also according to Wikipedia, the KNC basically runs its own militias now, and they seem to be largely backed by Turkey:
The KNC leader claimed that partially in response to the military power of the PYD, the KNC formed its own paramilitary wing, the Rojava Peshmerga. [...] Due to the political tensions between PYD and KNC, and low manpower comparing to the People's Protection Units, the Rojava Peshmerga haven't been able to enter in Syria. [...] On 17 December 2018, US envoy to Syria James Jeffrey informed the press that some Rojava Peshmergas have been deployed across the Iraq–Syria border. The continuing disputes between the PYD and KNC, however, are still preventing the Rojava Peshmergas entering Rojava despite the involvement of the international community. One of the main obstacles have been the KNC's links with Turkey and the fear of local people that the Peshmergas could be used against Rojava in future. Several independent and international sources have described them as 'mercenaries' supported by Turkey.
So that basically means the YPG has nothing to do with KNC anymore, the PYD being apparently their only real political representation.
Does the US have a better opinion of the other Kurdish parties, e.g. the KNC? Have US governmental organisations labelled any other Kurdish political parties (not militias) as terrorist or as affiliated with terrorists?