Best strategy to populate index from multiple other indices with point in time integrity

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OpenSearch 2.13.0

Describe the issue:
I have a system with multiple indexes, some are fed once a day using csv file ingestion. Some others are real time through kafka. For reporting purposes, I have one index that combine some information from said indices.
I’m trying to figure out if someone works on a similar infrastructure and is willing to share the strategy used.
The most tricky part of the problem is, for example, a business log. a client might purchase some product on a store. Imagine now his file has a phone number and he changes the phone number during the day. the business log report must keep the number he had at the time of the purchase so I really need to guarantee the sync of all indices at the exact time I log that document.

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