The "Thain's Book" translation is often read by non-specialists in the period as a complete and accurate description of events at the end of the Third Age. More accurately, it should be considered as a group of sometimes self-contradictory sources, none of which survive in the original. This group of texts had at least three authors, one of whom later admitted he had lied in his original account, and later amended it. The material has certainly been recopied and 'corrected' several times by much later writers. It occasionally deals with matters, such as the history of the dwarf-kingdoms and the political organisation of Northern Rhovanion, of which none of the original authors had much understanding or experience.
In this context, it is pleasing to discover that the recent movie based on the life of Bilbo Baggins (or Mad Baggins, as he is usually referred to in later Westron sources originating from the Shire) has called on material beyond Professor Tolkien's English translations. I believe this to include material available until recently only in Khuzdul, and now of course, translated into modern Croatian as the nearest equivalent modern European language. I also noted elements of a version of the legend that to my knowledge, is preserved only in material written in the most obscure dialects of Sindarin, and now held in the archives office in Machynlleth.
The sources for this period that originate from outside the Shire are of course also problematic in many ways. Like the Thain's book, they are often self-contradictory, particularly on the important but almost undocumented area of Dwarf military organisation and economic development. Source preservation has been poor, particularly in the case of the document that is thought to be Balin's personal diary, available today only in the most fragmentary and puzzling form. Re-copying has added errors, particularly to the Khuzdul sources which are notoriously difficult to transcribe quickly or accurately. The Sindarin material probably glamorises life in Rivendell and accentuates the military power of the Sindarin-Noldorin remnant living there - but it may still be more accurate than the Shire-version, which was very clearly written by a hobbit who had at that time no grasp at all of any of the Elvish languages.
None the less, such attention to detail is most unexpected in a movie made for the entertainment of the masses, and deserves to be recognised and commended. I look forward eagerly to the planned future works, and particularly to the release of the full bibliography.