What are your approaches to finding manuscripts online

[ReneZ]

Marci's life has been studied intensively by Czech historians, for well over a hundred years. It is based on precisely the sort of archival research that this thread is about.
The sources I quote at his You are not allowed to view links. Register or Login to view. may illustrate this. This also provides the entirely reliable reference for the Zahan monastery statement I made above.

I think the chance is high that some known and digitized manuscripts have relevance for the VM, but this relevance hasn't been noticed yet. But then I'm thinking about something relatively small, like an illuminating parallel for an image.

I remain very sceptical about such parallels. Many are subjective (are vague, or involve some theory or hypothesis) and many are generic (yes, the Voynich MS sagittarius fits in a German tradition).
The most objective and specific comparison that I can think of, that has been made until now, is the anatomically incorrect lobster. 

However, there is extremely little that can be concluded from this, because we have a very incomplete picture of where and when such incorrect illustrations appeared.

We would need something much more complete – not a single detail – and unkown, undiscussed illustrated manuscripts are getting more and more rare as time goes by.