Don’t beat yourself up over this. It recently happened to my mother who is usually on top of these things and the etiquette that goes along with it. She was recently in contact with a friend about the passing of a mutual acquaintance. She hadn’t been in contact with this person since late last year and inquired about her very ill husband. It turns out he passed away at the beginning of the year. My mom was shocked to hear this and said she had no idea and didn’t see the obituary. It turned out a lot of probably didn’t know because the newspaper screwed up printing the obituary!