The Book Switch Theory

[eggyk]

Well it's not completely nonsense -- There is a straightforward and mathematically precise approach to combine the probability distributions to form a proper combined distribution.  It does, however, require additional information (without which, one must resort to the adopting of specific assumptions.). Once one adopts the specific assumption that the separate samples are all from a single source (i.e. all the parchment samples are indeed from the same animal slaughter), then the mathematical combination of probabilities is deterministic. But the technicians really should have been explicit about the fact that this was an adopted assumption, and that it is under that specific assumption (and only under it), that a combined probability distribution can be derived. 

Yes, to be clear I think the underlying assumption (that they are from one object) is nonsense, or is wrong or flawed.

The statistical work done after that assumption was made is fine, as far as I can tell. That being said their exact methodology and error handling was not published.