I know that this question has been answered to some degree through other posts, but my question is this:
If my type-D visa to Portugal is valid as of April 16th, 2017, may I enter Portugal or any other Schengen country prior to this date under the terms of the 90-out-of-180 day tourist visa waiver granted to US citizens? That answer seems to be a relatively straightforward "yes" - anyone disagree?
Specifically, if I were to enter Portugal or another Schengen country before my type-d visa was in effect (let's say March 15th, for example), and got my passport stamped at port of entry as a normal US tourist, how then, come April 16th, would I "activate" the visa? Would I need to leave the country/Schengen zone and come back in order to have border control see and stamp/activate my visa or would it be assumed, if I was already in the country, that as of April 16th the visa becomes valid and I would have to do nothing? If I was in a different Schengen country - Spain for example - how would I then register my presence in Portugal as of April 16th since there are no border checks between Schengen countries?
If anyone understands and can explain the mechanics of this, I would be very grateful. I can understand the legality of coming in advance because I have that privilege anyways in the Schengen zone as a US citizen, but how to then migrate from tourist status to active visa status - do I need to do anything? Thanks.