How to square handwriting variation?

[LisaFaginDavis]

This is a fundamental methodological question about paleography. When are variants attributable to scribes being human and therefore inconsistent, and when do they signal a change of hand? Unfortunately, there are no good answers. Paleography is inherently subjective. If you stare at any handwritten book long enough, you can convince yourself that there are 300 scribes or only one. There is, of course, an objective truth, but that truth can often only be expressed as an opinion. 

In my own work researching, describing, and cataloguing hundreds of medieval and Renaissance manuscripts over the last 35 years, consideration of the number of scribal hands in a manuscript has always been a critical component. Every paleographer has their own style and has to make their own decisions about when to interpret a sample as the same scribe or a different one, based on experience, general appearance, codicological considerations, and specific letterforms. Having a sense of which letterforms are going to be useful for distinguishing hands is something that comes with experience and time, and the useful diagnostic forms vary by place and time. For example, in a late medieval manuscript from England, I would refer to the [a] and the [g] in particular. In 12th-century Germany, I'd look at [&], [ct], and [g]. In 10th-c. France, I'd consider different forms. 

For the Voynich, we are in uncharted waters, since there are no dated and localized manuscripts in the script for us to compare. And so we have to draw conclusions based on comparisons to other types of scripts (such as Humanistic Bookhand) and by considering letterforms carefully. But none of that helps us decide if two EVA [d]s that are near one another but look somewhat different from one another are by the same hand. They might be, they might not be. My own determination is that each page (with the exception of 115r), most leaves, and most bifolia in the manuscript is/are each attributable to a single scribe. I stand by that work, but no one is obliged to agree with me.

I'm sorry I can't be more helpful, but this is a question that professional paleographers have been debating for decades. Ultimately, it comes down to the fact that scribes are human. Being human means that they are inconsistent. It's also what makes manuscripts so delightful.