Regarding your apparent primary concern
about the unavailability of the original manuscripts, rigorous and
skeptical testing of the consistency of the extant earliest copies of those originals has not jeopardized their
accuracy.
Consistent with the previous analyses at
Skeptical Science, RFC12 finds that the climate models used in the IPCC 2001 Third Assessment Report (TAR) and 2007 Fourth Assessment Report (AR4) predicted the ensuing global surface warming to a high degree of
accuracy, while their central sea level rise predictions were too low by
about 60 %.