One thing that might help (or not, depending

) is if you started out by defining your land areas. Start with the main Kingdom, then subdivide it in to a few Duchies, then those into Baronies and so on.
As a rule, unless the kingdom is being built from the ground up, the land demarcations will predate the people in charge. This means that the titles a person holds depends entirely on the lands he rules...not vice versa. Lands are granted by heredity, marriage or by royal fiat for services to the crown (generally speaking this is done fairly rarely, as the King can only give away lands that he is the direct lord of...he can't make you the Baron of Exeter if there's already a Baron of Exeter (unless something HAPPENS to the current one, but that's a whole other issue

)). Once you have a map of what titles are -possible- in your kingdom, that helps narrow down who has what. Remember it's not at all uncommon for nobles to have many titles, because they're lords of many lands. The Duke of Sulzbery might also be Baron of Pludon Mound and Earl of Breton...or more! Generally speaking, the longer and better his war record, the more wives he's had (not at once, obviously

), and the older his family...the more lands he'll have titles to.
Land boundaries were often based on titles that were decades to centuries old, using vague directions and physical landmarks (rivers, forests, mountains) that might or might not be exactly as described in the document. This is one reason there was so much squabbling between nobles in that period of history. I say this only to bring up the potential as adventure hook, and to illustrate that when drawing land boundaries, it's not a bad idea to base them on geographical features of the land on the map.