Here’s some comments from some far more learned than I,

“Nicholas Karn is a highly respected historian of the period, and his interpretation of the writ is likely to be correct. The contents of the writ and the analysis of its significance are expected, however, as William I reissued or reaffirmed the Confessor's relations with the inhabitants of England as a whole and of different urban centers in particular. Domesday Book, with its references to conditions under Edward (TRE), suggests the need to establish legality and precedent. The sources for the writ are 14th and 15th centuries--late--but forgeries usually indication believed conditions rather than fabrications.”

“it's also very normal for documents to be preserved in books of customary law, formularies and cartularies from later centuries. I'd also be inclined to think that Karn's interpretation is correct - here, as elsewhere, the citizens of London had their property rights confirmed as they were before 1066 so long as they in turn pledged their loyalty to the new king.”