Every company, and the annual report its figures came from

"Source: SEC filings" names a category, not a source. Six pages in this section aggregate 375 companies' annual reports, and the only version of that claim a reader can check is the list of which companies and which reports. That is this page: every company in the universe, its sector, and a link to the filing on EDGAR.

The universe is a market-cap cut rather than an index. Index membership is a licensed list that changes for reasons that have nothing to do with the companies in it; a cut at 28 billion dollars is something anyone can reproduce from the method note. Dual share classes are collapsed to one line, so no company is counted twice.

125 companies were removed as foreign private issuers. Three tests are applied together — the ADR flag, an annual report on Form 20-F or 40-F, and a reporting currency other than the dollar — because no one of them catches everything: the currency test is what caught Toyota and Ecopetrol reporting in yen and pesos, and the form-type test is what keeps Accenture and Linde in, since they are incorporated abroad and file a 10-K like any US company.

Coverage is not uniform and the pages say so where it matters. 366 of these companies disclose an employee count; 204 publish a geographic revenue split that resolves into US and non-US. A figure computed over a subset is only worth quoting if the subset is stated, which is why every table in this group carries its own count.