calendar entries gone after update ios 6.1.2

With the Iphone 4S and the Ipad 3 i an using icloud.

All conatcts and calendar entries were synchronisized.

After the update to Ios 6.1.2 most of the calendar entries disappeared.

The last backup on my Macbook was done in december 2012.

After connecting the Iphone to the macbook, a new backup was created.

In the itunes selection the backup from december 2012 is not visible any more.

Additional the search for the backup files on the Macbook was without any results.

The folder name */MobileSync/Backup/ is not visible for spotlight.

Does anyone have an idea how to proceed to get the calendar entries back ?

The only available backup has the actual status with the missing data.