Well, it depends. I lost my two cousins in the previous couple of months but they don't come to my mind often because I wasn't attached to them.
Whereas my grandmother passed away in 2017 and I still remember her like it was just yesterday's incident. I don't do this birthday thing of the dead ones
People remember, or don't remember those who pass on depending upon their relationship they had with the person in life I guess, as you have demonstrated. I have cousins I've never met for instance, similar to your situation. When they die, or when I die neither them or I will be too fussed about it I guess.