Presumably this isn't actually true though? Like if you buy 5 shares, someone else's brokerage account goes down by 5 shares at the same time. The transaction is recorded on both sides, isn't it? Should be possible to establish who the seller was.
My belief here is based solely on having read some documents about the assignment process and having seen no reference to such record-keeping.
https://www.theocc.com/getmedia/0cdda3c2-ab81-450f-b8b8-7ce8... https://gdcdyn.interactivebrokers.com/Universal/servlet/Regi...