Another early riser mmzz!
It will be much easier the second time around for all the reasons you state, but I think the biggest difference will be knowing the likely grade boundaries (although I do think they will still be rising year on year in 2020). Both of my DC's schools have tended to under-grade mocks, probably in an attempt to avoid complacency, but I'd much rather look them up for myself to get a real picture of where they're at.
I can't believe you got a call from the HoY. Mr Persistent maths teacher clearly has control issues. I wonder what would have happened if your DH had dealt with him from the off. I suspect it would have played out very differently. That sort often have a problem with women with a point of view, particularly when it differs from their own!
I won't be on the 2020 gcse thread (DS is my youngest) but I'm hoping we can keep this thread going through Y12/13, albeit probably at a slower pace!
Anyway, we've still got GCSEs to finish first! 3 more for DS next week and he's done. And the World Cup begins! Thank god it didn't start 2 weeks earlier...