Yeah, you could get an unlisted number but you were charged for it and almost no one did because it was also how people you wanted to get in touch with you found you a lot of the time. Not that data breaches aren't bad but a lot of the breached info has been pretty routinely available for a very long time. (And, as you say, cell phone numbers are probably less routinely available than landlines were.)

I don't go out of my way to publish my cell or address but a lot of people have them.

My old man was a doctor and the local phone company at the time (GTE) automatically made our home number unlisted. Presumably this was done for other “critical” professions who might receive many home calls that should be directed at their place of work.

Being unlisted was sometimes devastating to a 1980s kid’s social life… I missed out on multiple birthday parties and other invitations. My sisters probably lost out on some dating opportunities.

nonetheless, pre-opting, your information was there, so anyone with a phonebook from before you made that decision would have your information. if an organisation had an interest in invading people's privacy it would not be complex to simply keep a copy of every edition of the phonebook

so what you could opt-out? your info was/is still in any phonebook from before you opted out. any well-prepared organisation, which these modern data-collection firms are, would have no problem whatsoever keeping every edition of the phonebook for this purpose.

yeah the discrepancy is that its harder now. phonebooks were essentially free and had people's addresses in them