This may be a little better.
(index=some_index source="log_source") OR (index=some_index source="log_source" "Not Updated - sourceId" )
| eval Rejected = if (match(_raw, "Not Updated - sourceId"), 1, 0)
| rex ".*Batch info: completed, processed entities: (?<numberOfMessage>.*)"
| stats sum(Rejected) as RejectedEvents, sum(numberOfMessage) as ProcessedEvents
| eval total = ProcessedEvents + RejectedEvents
| fields total
If this reply helps you, Karma would be appreciated.