iDash creates a subscription for real time events, and as jobs move through the queues in CA7, we collect those events.
When we get an event that tells us a run finished, good or otherwise, we write that to our db.
If iDash was down for an extended period, then we would not have gotten the events to write to our tables to report on later.
We do have a recovery mechanism for short down times, using ENF on the mainframe to store and forward events, but that typically can only hold 2-3 days worth of events before they begin rolling off.
Concerning your questions:
1: How does iDash get job log data from CA7?
==> It doesn't get log. it only gets current events as they are created.
2. What would cause date ranges to be missing? Are there known issues or scenarios that can cause this in your experience?
==> See above explanation. Probably iDash wasn't running at those moments.