The service frequencies shown are the ones used in the full business case. They don't have to be what is actually delivered, more can be done on top of that. We are not going into the 2029 and 2031 timetables blind either, there's already planning which shows the peak turnbucks at Tring (5), Bletchley (2), Milton Keynes Central, Northampton and Rugby (1 each). 2 services an hour for the Trent Valley and 4 via Birmingham, but exactly where they run to is clearly open for debate. But as this is a decade in the future there's plenty of time to manage it out.
I find it hard to believe that the HS2 Stoke-on-Trent and Macclesfield service will terminate at Macclesfield rather than continuing to Manchester, as well as the other mentions around the Lancaster service, which I also think should call at Birmingham Interchange. What exactly will happen to this service with respect of phase 2a and the Handsacre connection though, I don't know.
The other interesting thing is that it's now expected for High Speed services to launch from Old Oak Common in 2029. The current Avanti West Coast franchise only runs to March 3031, so by the time they reach London Euston they may not even be around an more.