The "alarm history" feature in the mobile app appears to pull from the "timeline" database of win911 control center. This limits it to 200 events. If you have a large system, that timeline will be lucky to show more than 24hours of events. Meaning the "alarm history" feature in the app is essentially useless except for small systems. If you let us search 1 month in the past for alarm history, it should be able to query every alarm from that time span.
There is no hard time limit on the data that is available on the alarm history tab, nor is there a limit on the number of records that can be displayed in SmartSights Mobile. The range of history retained is configurable in WIN-911 Workspace in the Mobile Gateway settings (in days).