Another vote for updates, and you may even say if they would prefer not to receive them just to let you know and it won't hurt your feelings, otherwise you'd be happy to send them every so often.
I am FB friends with the owners of my very, very favorite shelter dogs that I would have adopted in a second. I love seeing them on my feed. Shambles play dates with one of my ultimate favorites. Shambles' "breeder" or whatever that technicality is obviously gets constant updates via FB. I have no idea where every one else came from before the shelter/rescue. Magpie was a seizure, so I wouldn't want to contact her previous family if I could. Smalls is old enough no one works at the shelter she came from that would remember her. The rescue Jack and Jonas came from is full of lunatics and I avoid them at all costs now that I know, and ignored the few updates I did send. I tracked down the breeder Jonas came from before he landed in a mill and they didn't give a ****, just tried to sell me his sister right away. I hate the SPCA Elsa came from with every fiber of my being so.