You’re correct. AMBOSS mentions this here https://next.amboss.com/us/article/3g0SE2#Y2e99f44f4d330972da0774059ae5846c.
I think that this is sufficiently covered by nid:1523243276095 though. If needed here, we could add “Elevated HbA1C could also be due to increased RBC lifespan due to another medical condition” to simplify this.