BRIN lazily summarizes blocks _at the end of the table_. When you build the index (by either creating or reindexing, concurrently or not) it will generate summa

BRIN lazily summarizes blocks _at the end of the table_. When you build the index (by either creating or reindexing, concurrently or not) it will generate summaries for all full block ranges of the table. As such, it is possible that even a BRIN index was corrupted by concurrent reindex in PG14 < 14.4 because it didn't receive all tuples that it should have summarized.