Charlemagne - This is a general question (not about Charlemagne) about prepositions in titles

I don't know of a general discussion forum, so I figured that I would post it at the most popular profile. :)

It seems that the prepositions for German & Dutch titles are all over the place. Unlike for French & Spanish (and their various historical dialects), which use "de" or the plural "des" for everything, there seem to be a number of different ways to do the preposition for titles in German & Dutch.

For "Herzog", I've seen "von", "zur", "zu", "der", and for "Hertog", I've seen "van" ("aan" seems to be a proper translation of "zu"). For "Graf", I've seen "von", "im", "zu", and for "Graaf" I've seen "van", "in". For "Herr", I've seen "von", "zur". In some Dutch profiles, I've seen "aan der", and there are probably more out there that I have forgotten about.

The point is, it seems that there should be a standard way to do this. I am not sure what sources everyone is using for profiles, but I have a hunch that folks are just using whatever is in the sources, and thus I have to wonder if the sources have it correct. Surely, there must be some systematic way to do these.