I usually don't remember. My NT DH doesn't remember either. We just say "Hi! How are you?" if someone looks familiar.
Occasionally that someone might be a complete stranger who look like people we've met, but it doesn't hurt to say hi to them.
In that aspect I'm so glad to be an adult in North America, everyone is my equal. As a kid who grew up in China, we're supposed to call everyone their proper names and titles, like elder paternal uncle Wu, teacher Lee, great maternal aunt Hsia...etc. I often called people wrong names. Like calling my mom's best friend's husband elder maternal uncle.
This extend to all your parents friends and co-workers, though the rules are not fixed. Like for all the females you call them maternal aunt, you don't need to know their age. For all the males you call them elder or younger paternal uncles, you need to find out their age compared to your dad's. You also have to remember who's older than who among your relatives and peers. If a kid is born a few hours earlier than you on the same day, you gotta call him elder brother.
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AQ score: 44
Aspie mom to two autistic sons (23 & 22)