Adds up to 100 more backlink rows found by the second index, marked link_source=second_index and carrying the spam_score and source_page_score the first index does not report. That 100 is the source's own ceiling, not a setting: asking for more returns the same hundred, whatever the domain. They barely overlap the first index, on a test domain only 2 of its 100 referring domains were already present, and the rest skew toward link networks, which is what a spam audit is looking for. Rows identical on url_from, url_to and anchor text are dropped. It needs the per-link records switch above to be on, it does not raise backlink_sources because this is the same index the second_* columns came from, and every extra row is billed, so cap the total with maxBacklinks or turn this off for the first index alone.