I have the following specific case but it would be nice to have a general answer if one does exist:
A fellow German traveler just spent 3 months in Turkey on his passport. He just then left to Bulgaria, the rule is to wait three months before he could enter for another three months. But Germans can enter Turkey with just their ID card or if they have, a second passport, so he is going to try using his ID when going back to Turkey tomorrow.
Is there a way for the Turkish border authorities to link the two different Passports/IDs and see that he is not really allowed to enter?
I guess the name and date of birth is the same on both, but that is not unique enough.
I am sure German authorities could link the two papers but can it be done by foreign countries?