Calendar Events Prior to February 2010

[samosIM]

I have an iPhone 6 and an iPad Air 2. I am using both Calendars and the latest version of Calendars 5 from Readdle. My events from January 2010 and earlier are not available. I am not certain when I lost the ability to view these events. I may have last looked in January or February 2016.

What happened to these events? Is there a way to retrieve them? I've looked at all settings I could find on my 15" Retina MacBook Pro, my iPhone and my iPad Air, but to no avail. Is there a setting somewhere that allows you to save all entered events as far back as I have used a Mac?