Socks came to us from Random Rescue at an age of about one year old, and all we knew about her was that she'd been with Random Rescue for about a month (as I recall) and before that had come up to Vermont from Mississippi, where her previous owner was an older woman who had to give her up because she was going into a care facility. We're not even sure what her breed is: visually she looks like a black lab, period, but it's been speculated that she's a mix of that and something else, perhaps Australian shepherd. (Since there's no clear visual indication, we only pretend to be more certain than we really can be.)
After we'd had her for a couple of months, I contacted Random Rescue to ask if there was any way to get word back to her previous owner. I figured that if it were me who had to give my dog up to a rescue agency, I'd want to know how she did, and would be delighted to receive word that she'd found a healthy, happy home. And in the age of the Internet, there's no reason we should be unable to get in touch with the right people in Mississippi. Heck, it should be fairly easy to send photos or even video. About the only reason that should stop it is if the other person prefers not to be contacted, or isn't able to be contacted due to health concerns.
However, my efforts went nowhere. Random Rescue referred me to the agency in Mississippi from whom Socks came to them, who didn't respond to their email for a while, but when they did, they seemed to think it was a great idea, and promised to try to get in touch with the previous owner. They didn't tell me anything about her, which is as it should be -- it should be up to her to decide whether to let herself be contacted. But then we never heard back. I sent off one more "hi, did this fall through the cracks?" email, but when that didn't get answered, I dropped it. No way to tell if the rescue organization just was too busy, or if the former owner couldn't or didn't want to be contacted.
So not only can't we get word to her (though it's possible the rescue people did at least get to say "she's in a good home in Vermont" at least), we have no chance of finding anything about her past. Was she a city dog or a country dog? Did she have other dogs she lived with? What came of her litter? For that matter, what was her birthday, what's her actual breed, things like that? I wish we could find these things out. But I guess we'll just have to be content without knowing.