I have applied for a National visa to Germany. In the meantime I also have a multiple entry Schengen visa that is still valid. If I get the national visa, say from 15 August, but I want to enter the country before that, can I do that on the Schengen visa?
Technically yes, I received this answer from the Austrian BMI (Bundesministerium für Inneres) regarding visa-free to visa D transition which should also be applicable to those holding C visas: "If the visa-free stay is short or the travel purpose for the visa-free stay is different from the one for the visa D stay (eg first tourism, then study/employment), the entry would be lawful. Whereby a visa-free entry (observing the rule: 90 days per period of 180 days) and the subsequent stay with a visa D is seamlessly possible."*
*This was translated by me from german and should be used for informational purposes only...