How to Retrieve Calendar Records in Exchange Server?

Hello everyone. First, I have a few information to trade. I set up our emails few years ago and did not have any problems at all. Every person in our company has no timetable for its creation.
It was installed through a browser and then it "exchangeserverip/exchange"
We also have a secretary to access the calendar that we can view, update, delete, etc. The only way to connect to the timetable is as follows: the use of an iPad and iPhone and Blackberry applications. This has been working very well so far.
Few weeks ago, he called me and told me that the record in the calendar was gone except for the record on the last three months. I looked at the calendar by myself in the only way he knew (which was from the browser) and saw that he was right, everything was lost.
And also occurred in the heads of two devices that it was all missing. No change in iPads and nothing (to my knowledge) has changed in the Blackberry as well. It does not use any version of Outlook for email (which is largely an office of Thunderbird).
Any idea why there are only 3 months of programming available now?
And most importantly, is there any possibility that the missing years are still in stock somewhere and just not shown?
Thank you.
