On the Internal Witness of Scriptures
I think it is very erroneous to assume that the internal witness of Scripture is unreliable unless supported by external (or extra biblical) testimony.
1. When witnesses to an account are two or more, the testimony already carries a level of reliability. The Pentateuch, Kings, Chronicles, Prophets, Gospels contain accounts by varying sources that can be cross-referenced to gain a fair historical picture.
2. Cases of sole testimony cannot be disregarded as totally unreliable as per the rule of truth-expression. To stipulate that one must not testify or witness unless his/her experience is shared by others is to impose a gag on truth-expression or the possibility of hearing truth. In fact, it is a sealing of self from the possible sole source of information. Sole testimony, however, is also open to challenge if there can be enough reasons for raising such a challenge. But, in the most central narratives in Scripture, the witness party includes several persons. Thus, as per #1, the combined testimony of all these witnesses demands a hearing.