On my iPad, Calendar doesn't show all events (from all of history) from my Google calendars. Only the last 1.5 months or so.
I had the same issue with iCloud calendars, but when I changed the sync duration setting in Settings → Calendar, the problem got fixed.
However, I still only see recent events from my Google calendars.
Best Answer
What I encountered was a simple bug, not a GCal limitation.
What I did was removed Google Calendar completely from my iPad, then re-enabled it, waited until all was downloaded, and voila.
Phew!