Since "vrai" is an adjectif and "yes" is not, I'm guessing that its meaning become not really the same. Here's the example:
A: Bonjour ! Vous avez l'air très fatiguée C!
B: C'est vrai ! Pourquoi ?
C: Je n'ai pas pu dormir la nuit dernière.
and translated to:
A: Hello! you look so tired C!
B: Yes! What happened?
C: I couldn't sleep last night.
But I can't find the reason why the meaning feels different. Therefore I'm confused, is there actually any glissement or not?