I'm assuming the regex is fine, as you seem happy with that, so in terms of efficiency, if this is a one-off operation, does efficiency matter?
Your query is searching yesterday. Is the intention that it searches further back than that? Could you just run a backfill operation and let Splunk handle the scheduling?
If you're looking for a general solution, then you could output each production index search to a CSV (outputlookup append=t) and then after running all the searches, just inputlookup the csv and stats count on the data.
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