This set of changes improves the Listevents API.
Before, Listevents only queries Stripe for the last X number of events. However, after Stripe started enforcing a limit of only 30 days for the number of events you can request, this API call became less useful.
Now, the API call can optionally query the civicrm_system_log table, which goes back farther.
It also allows the user to specify a subscription id and only display results for the given subscription - including results in the system log and also all the charges for the given subscription according to Stripe.
Lastly, you can filter out all charges that are properly processed in CiviCRM.
Now it's much easier to use Listevents to find contributions that are processed by stripe, but not properly processed in CiviCRM.