562 companies, every one of them researched in both directions: what it owns, and who owns it. The number is not 500, and the two reasons are worth knowing before you go looking for something that is not here.

Tickers are not companies. The index lists 567 ticker rows but 564 companies, because 3of those rows are a second share class of a company already in the list: Alphabet is both GOOGL and GOOG, Fox is FOXA and FOX, News Corp is NWSA and NWS. Each of those pairs is one company with one page and one ownership register, because both classes are issued by a single filer and managers report them under that one identity. Where the two classes differ in voting power, the company’s own page says so rather than splitting it in two.

5 companies here have no ownership register: AZUL SA, FedEx Freight, Honeywell Aerospace, Parabilis Medicines, Inc., X-Energy. Not an oversight, and not a matching failure. FedEx Freight and Honeywell Aerospace are newly separated registrants with a brand-new filing identity, and managers still report only the former parent, so there is nothing yet to aggregate. AZUL SA and Parabilis Medicines, Inc. and X-Energy listed after this snapshot was taken, so no manager had reported them yet when the quarter closed. That is the ordinary first state of a newly public company rather than a gap in the data. None is given another company’s register, which would credit it with holdings nobody reported. That leaves 558 registers built from 564 companies, and those figures are reconciled on every build rather than asserted.

64 companies here are not in the index at all, and they are included because ownership does not stop at a US index. Absci Corp (held by 1 of the researched companies), Aktis Oncology, Inc. (held by 2 of the researched companies), Allogene Therapeutics, Inc. (held by 1 of the researched companies), Ally Financial Inc., Archer Aviation Inc. (held by 1 of the researched companies), Arcus Biosciences, Inc. (held by 1 of the researched companies), Ardent Health, Inc. (held by 1 of the researched companies), ARVINAS, INC. (held by 1 of the researched companies), ASML Holding N.V., ASSEMBLY BIOSCIENCES, INC. (held by 2 of the researched companies), Astera Labs, Inc. (held by 1 of the researched companies), Aurora Innovation, Inc. (held by 1 of the researched companies), BETA Technologies, Inc. (held by 2 of the researched companies), Biohaven Ltd. (held by 1 of the researched companies), Caribou Biosciences, Inc. (held by 1 of the researched companies), Celcuity Inc. (held by 1 of the researched companies), Cellebrite DI Ltd., Contineum Therapeutics, Inc. (held by 1 of the researched companies), Corebridge Financial, Inc., CoreWeave, Inc. (held by 2 of the researched companies), Eikon Therapeutics, Inc. (held by 1 of the researched companies), ENBRIDGE INC, Energy Transfer LP (held by 1 of the researched companies), ENTERPRISE PRODUCTS PARTNERS L.P. (held by 1 of the researched companies), Entrada Therapeutics, Inc. (held by 1 of the researched companies), Global Business Travel Group, Inc. (held by 2 of the researched companies), Hyliion Holdings Corp., Intellia Therapeutics, Inc., Jefferies Financial Group Inc. (held by 1 of the researched companies), Joby Aviation, Inc. (held by 1 of the researched companies), Klarna Group plc (held by 1 of the researched companies), Kymera Therapeutics, Inc. (held by 1 of the researched companies), Kyverna Therapeutics, Inc. (held by 1 of the researched companies), Legence Corp., Legend Biotech Corp (held by 1 of the researched companies), Liberty Live Holdings, Inc. (held by 2 of the researched companies), LOUISIANA-PACIFIC CORP (held by 5 of the researched companies), Lucid Group, Inc. (held by 1 of the researched companies), Macy's, Inc. (held by 1 of the researched companies), MeiraGTx Holdings plc (held by 1 of the researched companies), Mobileye Global Inc. (held by 2 of the researched companies), NEW YORK TIMES CO (held by 2 of the researched companies), Opendoor Technologies Inc., Oric Pharmaceuticals, Inc. (held by 1 of the researched companies), Personalis, Inc. (held by 1 of the researched companies), Protagonist Therapeutics, Inc (held by 1 of the researched companies), Pyxis Oncology, Inc. (held by 1 of the researched companies), Rapport Therapeutics, Inc. (held by 1 of the researched companies), Republic Airways Holdings (held by 5 of the researched companies), Rivian Automotive, Inc. (held by 2 of the researched companies), Robinhood Ventures Fund I (held by 1 of the researched companies), Samsung Electronics Co., Ltd., SANMINA CORP (held by 1 of the researched companies), Saudi Arabian Oil Company (Saudi Aramco) (held by 1 of the researched companies), SIRIUS XM HOLDINGS INC. (held by 1 of the researched companies), SK hynix Inc., SpaceX (held by 7 of the researched companies), Spero Therapeutics, Inc. (held by 2 of the researched companies), Symbotic Inc. (held by 1 of the researched companies), Taiwan Semiconductor Manufacturing Company Limited, WaterBridge Infrastructure LLC (held by 1 of the researched companies), Wave Life Sciences, Inc. (held by 1 of the researched companies), Xanadu Quantum Technologies (held by 2 of the researched companies) and Zentalis Pharmaceuticals, Inc. (held by 1 of the researched companies). The ones marked as held are here because the researched set owns pieces of them, so leaving them out would have drawn those stakes pointing at nothing. Others are the largest companies outside the index in semiconductors and energy, and their registers show something no S&P 500 constituent does: control held by a state, a founding family or a web of affiliated companies rather than by index funds. The newest arrivals are companies that simply listed: an IPO, a de-SPAC or a merger gives a company a ticker long before any index takes it, and a company with a ticker is public whether or not it is ever a constituent. Until that happened, each of those was a page here headed “private company”, telling you no 13F could see it directly above figures that came from 13Fs.

Every figure on this site carries the filing it came from and the date it was measured. Where nobody has published a number, it is left unsized rather than estimated. How the register data is built, and what it misses.