1 Nephi 5:16

16 And thus my father, Lehi, did discover the genealogy of his fathers. And Laban also was a descendant of Joseph, wherefore he and his fathers had kept the records.

I wonder how much Lehi knew about his genealogy before he read the brass plates. When he first told Nephi about them (1 Nephi 3:3–6) he said “Laban hath the record of the Jews, and also a record of my forefathers,” which could have been a reference to Jacob, which would have been a general record of the forefathers of all the tribes of Israel. It makes sense to me that “the record of the Jews” would reside with the tribe of Joseph, due to Joseph’s birthright. But this language makes it sound as if Lehi didn’t know why his genealogy should also be on these records, nor did he realize what he would find. Once the brass plates were brought back and Lehi had a chance to look them over, he found a “genealogy of his fathers; wherefore (for this reason) he knew that he was a descendent of Joseph.” (vs. 14) The word “wherefore” means “because of” or “therefore.” In other words, it seems that this record is the means of Lehi learning of his royal lineage, and maybe he didn’t know it before. This verse says that “thus…Lehi did discover the genealogy of his fathers.” So it seems he didn’t know that a) he was descended from the royal or birthright line of Joseph, and b)that he was related to Laban. Laban must have known, having access to the record, unless he just wasn’t aware that he had any living relatives. It is possible that this is another reason for him not wanting Lehi to have the record. If someone else were known to have the royal bloodline, it would weaken his political position.