On the other hand EH Bildu hasn't yet tried to court left-wing voters outside of its claimed territory.
That is a significant difference and it's highly unlikely that EH Bildu ever tries to court voters outside Euskal Herria (Euskadi, Navarre and the French Basque Country, i.e. the territories that would constitute the independent Basque state) in national elections. However, in EP elections Spain constitutes a single constituency. In order to garner some votes from other regions, in 2014 EH Bildu allied with other peripheral nationalists such as the Galician BNG. In the 2009 EP elections left-wing Basque separatists were banned from running, due to alleged ties to ETA. They opted to endorse list including a bunch of far-left extra-parliamentary organisations throughout Spain.
Another one is that Kurdish nationalists (BDP, currently Democratic Regions Party or DBP) don't advocate for an independent Kurdistan in SE Turkey, but focus their demands on regional autonomy and the recognition of Kurdish language, culture and identity. Dropping claims for independence can be seen (arguably) as a tactical move in order to survive pressure from the Turkish state, but in any case that turn is prior to the establishment of the HDP and also concerns the PKK. Since his capture, Abdullah Öcalan has abandoned Marxism-Leninism and advocates for a special form of "democratic confederalism".
Formally the HDP is a Turkish party -with a strong Kurd component, obviously- that embraces the cause of ethnic and religious minorities, women and marginalised groups -LGTB people, for instance- throughout Turkey. Quoting the Wikipedia, the HDP aims to "overcome the traditional Turkish versus Kurdish divide" as well "collectively represent people of all ethnic or religious backgrounds and to safeguard their civil liberties by bringing about direct democracy and an end to capitalist exploitation" and of course "increase democratic representation and decentralisation of power".
