When you buy a treasury from the government, YOU own the treasury as the transaction is done between you & the government. Who owns it when a treasury it bought on the secondary market thru a broker? Does the government even know the ownership has changed? Who really owns it? You? Your broker? Clearing Firm? Original Owner?
I am not sure what you are trying to figure out. You bought it, you own it, an old phrase. Does it really matter who’s the previous owner and why do you care?
Who owns the stock when you bought it from someone who's also bought it from someone else, who in turn got hers on the day of the IPO? Yeah, it's the same concept.
DTCC’s FICC will clear almost all of them by next year. CBES will probably be outdated soon but who knows. Your position is kept with the brokers.
What about brokered Bank CDs? Who owns those when transferred on the secondary market? Is there an industry wide book entry system for those too?