What I have to share is not precisely named or called a "claim to veracity"; however, I think it is what you are looking for in your question.
In the prefatory remarks (remarks which the author makes before his book or story begins) to Dracula, Bram Stoker makes the following statement:
How these papers have been placed in sequence will be made manifest in the reading of them. All needless matters have been eliminated, so that a history almost at variance with the possibilities of later-day belief may stand forth as simple fact. There is throughout no statement of past things wherein memory may err, for all the records chosen are exactly contemporary, given from the standpoints and within the range of knowledge of those who made them.
In essence, Stoker is assuring his readers that everything they are about to read is true. Each of the documents, letters, and other papers contained in the novel have all been placed in sequential order; everything that is unimportant ("needless matters") have been removed. This has all been done for the sake of his readers, of course, and because of these efforts, there can be absolutely no reason for any reader to doubt the veracity of what he reads. In fact, it is so clearly and precisely put forth that the events which transpire must be seen just as "simple facts."
Stoker goes one step further, assuring us that none of what we are about to read is blurred or marred by the fuzziness of memory; instead, everything was written contemporaneously (at the time it happened) by those to whom it happened.
The entire novel is comprised of a series of journal entries, letters, and other first-hand accounts by various people, so Stoker is obviously trying to reassure his readers that he has complied and organized them in such a way as to ensure that they are accurate (and therefore believable). Moreover, Stoker writes this in the hope that we will somehow read these fictional accounts (for both Stoker and his readers are quite aware that this is a work of fiction) as truth--which adds an even greater sense of horror to the story.
As to the "truth claims" you mention in your question, it seems to me that everything Stoker says in the prefatory comment is a truth claim which proves to be false. For example, he assures us that everything we are about to read is true, yet we know that everything we read is full of untruths, such as nearly everything Dracula claims to be true for himself and his history.
Perhaps you are looking for something more or different regarding the "truth claims," but I am confident that Stoker's prefatory remarks are exactly what you are looking for regarding the "claim to veracity." It may be that your copy or version of the novel does not contain the prefatory remarks, and I had trouble finding it in many online editions of the text, although I knew it existed. While I have given you the entire thing in the quote above, I also linked you to an e-text which contains Stoker's 1897 statement. Hope that helps!