So I had a phone call from my GP in response to the last of my emails. He has fixed my immunisations record, which now shows my two vaccinations on the correct dates. He explained that as Novavax has not yet been approved, it's not available as an option for him to record on my record. However, he said that this should not matter (a friend who has been vaccinated through the NHS has no other details on her record) and that eventually this information will be pulled down into my GP record from the main NHS Pinnacle system - it's just not a priority at the moment. Booster shots are more likely to be given to priority groups at a fixed point in time, rather than, say, one year after initial vaccination, so this will also not make a difference.
I feel better about all this now, but disappointed at the lack of communication from the trial team, particularly as some centres seem to be more proactive than others.