I synchronize my PerfectPace calendar with Google, Apple, Outlook or another third party calendar. However there are workouts missing that are available in my PerfectPace calendar.
PerfectPace synchronizes all your activites that are between the last 30 days and the next 365 days. Workouts that are outside this range will not be displayed.
Also Goolge, Apple etc. checks only every few hours if there is an update in the PerfectPace calendar so you might have to wait for some time for your activites to appear.