Compared to today, there were more trains from Amersham to London in 1977. There were some semi fast services (which from memory were not well loaded from Amersham owing to the longer journey time) which survived until the early 2000s and all the Aylesbury / Marylebone services stopped at Amersham, unlike today where some non stop Amersham. The same level of service was provided in the evenings for the return journey. The 9:34 service to Marylebone was the first cheap day ticket service, why a Met train ran 4 minutes after it always baffled me.
An extract from the Sunday service. No trains from Aylesbury to Marylebone, passengers had to change at Amersham, something that only changed in the past few years when Chiltern introduced through trains to Marylebone on Sundays. It was bad luck if you wanted to get from Aylesbury to London early in the morning, your first train appears to be 10:12!