He crowned himself king of the Serbs of Bosnia, the maritime lands etc.

Po milosti gospoda Boga kralj Srbljem Bosne, Primorja i k tomu.

No, you are wrong. Srbljem and Bosni are separated in his titulation. He used the title 'Srbljem' to denote the Serbian throne while ban/king of Bosnia ( Bosne/Bosni) was traditional title  in Bosnia. ;)

In the charter where Tvrtko speaks about his coronation he says that he is crowned with two crowns, one of God-given land of Bosnia and one of Nemanja family. Offcourse, when he speaks about his trip to the coronation site, he says that he went to 'Serbian land' ( srbskuju zemlu). ;)

before his death the title 'kralj Srbljem' was changed to 'kralj Raske' which means that he considered Serbs and Rascians to be the same, the words denoting the same "tribe".

There are charters where he numbers himself among Bosnians ( when I find more time , I will find it for you).

Now I am waiting for Ninoslav's charters and regnum servillie… :D