My wife and I are both writers. We’re also fans of stories: if we’re watching a mystery film, we try to figure it out. If we’re reading a sci-fi novel we’re thinking about how problems might be solved. If there are zombies involved we think about how we might get away!
And we cannot help but see Chekhov’s gun everywhere. Any time a the story makes a point of drawing attention to something we just know it is going to either be a problem or solve one later.
If a character says that they were a gymnast in high school, we know they’ll be backflipping out of danger before the end.
If someone remarks that their car is low on petrol, that means we know they are not going to reach their destination.
The movie Home Alone has Chekhov’s gold tooth!
Quite rightly, your viva has Chekhov’s thesis – OK, it’s your thesis, but the principle holds: it’s there to be used. It’s not just a ticket to get into the viva. It’s a resource that you can rely on to help you. At any point you can check something, clarify details and be sure of what you’ve presented.
In the earlier acts of your PhD you laid out your research in your thesis. In the final act, you can use it if you need to.