There are lots of things I don’t know about the viva.
I don’t know if there’s any great differences between the vivas of part-time and full-time PhDs.
I don’t know how well vivas over Skype work compared to vivas in person.
I don’t know what percentage of people submit a thesis-by-publication.
I don’t know all of the regulations for all of the universities in the UK. (but I’m working on it!)
And I don’t know what percentage of candidates fail their viva, because universities are very reluctant to share that sort of data.
I have theories or ideas about all of these; hunches based on incomplete information, or ideas about how to get more stats. I’d like to explore these topics and many others, I just need to find the time to do it.
But the information is out there.
On smaller scales, your personal scale, the information is out there. There are regulations for your institution. You have a supervisor who can help shape your expectations. There are graduates you can talk to about viva experiences.
Figure out what you don’t know about the viva, then get to work finding out more.
(and I’ll do the same!)