Older Exchange calendar disappear in Android Calendar, but not in Apple Calendar
Open system settings
Goto Users and accounts
Click on the exchange account
Click on Account settings
Click on the settings button next to the account name


Now you see all settings for this account. 


Scroll down
Click on "past items synchronisation"
Change this to all past items
Click the back button till you're out of the settings


NB: I translated "past items synchronisation", so the actual English name for this might be different, but I think it's clear what I mean. If you have the correct naming, then please comment here.