It's not silly at all! They would remember the person themselves, but not their name -- they'd need to be reintroduced to learn names, like before they met. To use your example, Lukas runs into Cinder for the first time and recognizes him for who he is, depending on your canonpoint, but he'd draw a blank on his name until he discovered or was told the work name. From there, he'd know him as Cinder.

Naturally, it's something you can handwave if you want, but we thought some people might have fun playing the frustration of reintroductions! I hope that makes sense.