Thanks everyone, appreciate all your insights.
As is so often in this whole enterprise, it seems there are gray areas, and people have directly conflicting experiences. Specifically here some needing to stamp, others not.
The area that seems very clear is the law needing you to be in on a Shengen, at biometrics time.
Of course, if biometrics was a few months after pre-approval, it wouldn’t really be an issue. But with it being an unknown amount of time, probably at least 6 months, but potentially 12, it really does create a problem.
I would be totally happy to leave PT to re-enter on a stamped Shengen, when the biometrics appointment comes up.
But it seems that if you enter PT, do get stamped, 3 months later you are effectively locked out of Europe. You would have overstayed. So you may exit PT fine, but now you have stamps showing an overstay, which creates problems. Even if you spent 3 months outside Shengen, to let it “recharge”.
So the whole idea of “you may stay in PT after pre-approval” should have this important rider “but only if you are happy to not go anywhere else in Shengen, for an unknown amount of time”. Or said differently, “if you care about travelling anywhere in Shengen before your card arrives, you might as well ignore pre-approval, it’s not conferring any additional benefits”.
Appreciate if anyone can correct any mistakes I’m making here. Thanks so much.