Many questions about the validity of the wording of the charters must lead historians into a study of their diplomatic, and that study must in turn lead them back to the question of how LL was compiled, for it is clear that many of the charters’ formulae were added during compilation, as seen by E. D. Jones, noting ‘the uniformity displayed over what we are asked to believe was a period of five centuries’. Similarly Brooke saw ‘a unity about these documents of a very exceptional kind, even for large collections of forgeries’ and concluded that:

Wendy Davies, in her paper ‘St Mary’s, Worcester and the Liber Landavensis’, demonstrated that some of the characteristic LL verbiage is parallelled in Hemming's Cartulary, which was compiled at Worcester ca 1095, and, without explicitly supporting Brooke's idea of a single presiding mind, noted the significant circumstance that Bishop Urban is said to have been a priest of Worcester. John Reuben Davies, however, has since shown that the relevant formulae are found widely among Anglo-Saxon cartularies. Without rejecting Urban and Worcester as a possibility, he is ‘inclined to suggest that the Anglo-Saxon features of the Llandaf charters are likely to have been formed by the “artistic” mind of, perhaps, a Caradog of Llancarfan, working from a general knowledge of Anglo-Saxon diplomatic’.

An invaluable tool for investigating the diplomatic of LL is Appendix I of Wendy Davies's The Llandaff Charters in which she lists the occurrences of all the major formulae in the charters. There are two drawbacks in the arrangement, however, which could not have been eliminated without the expense of a lot of space. One is that her Appendix I only shows one how the formulae are distributed through LL paginally (i.e. in the order of the manuscript), not how they are distributed chronologically (i.e. in the order of the Sequences), which is equally important in deciding whether they are editorial or original.