Assumptions baked into the VMS carbon dating

[eggyk]

The individual results do not have far larger ranges in the actual metric that was measured (y axis). All these samples are grouped together quite well, and I think the conclusions in the paper are the right ones - this strongly suggests a single object with a single narrow range of years. 

Yes they do? The individual folios had ranges of ±35 years. The final combined range has a range of ±15 years. That's a huge difference.

But this above is exactly what the actual values measured in the lab show, before it's artificially split in a bimodal distribution by the double-humped calibration curve. These curves above are what we should use to assess whether it's a single object or not, and not the computed time range.

These folios are literally not the same object. Just because they all potentially come from roughly the same set of decades does not make them so. 

Let's say hypothetically that we have another composite manuscript, with some pages from 1290AD, and some other seperate pages from 1330AD. If you were to test a few of the pages, and get these results: 

1) 1275-1335
2) 1285-1340
3) 1310-1352
4) 1320-1358

If you treat these as samples from the same object, you will get a tight range where they overlap of 1320-1335, and I think a similar range statistically. It would produce the wrong result. 
 

Would you rather think that the object was created somewhere in the yellow range, which would be consistent with all 4 measurements, or would you say that there likely were two different time ranges hidden there?

If this was one folio measured 4 times, I would of course assume the yellow range. But as this is 4 seperate objects, it's entirely plausible that they are two seperate time ranges.