I am surprised it had not happened sooner, because there had to be some, but today someone spotted an error in the section 21 notice flowchart – specifically in the end-note about s.21(4)(a) notices for tenancies that were periodic from the outset.
A corrected flowchart is now available here.
All other reports of errors gratefully received (more or less). Apologies to anyone lead astray – though thankfully it would not have been a fatal error.