Behind on 9m communication milestones - how unusual?

LO is 8.5m. Well ahead of all the 9m gross and fine motor skills milestones I see listed. Sits easily, crawls quickly, pulls to standing, has taken a few steps cruising or with a walker, picks things up and moves them around easily (for example, figured out a ball drop tower).

But doesn't really babble or converse in the traditional sense with baba, dada, mama sounds. Fusses, screeches, grunts, growls, etc. Makes more sound when concentrating on a new motor skill than when we're talking to them. Smiles, laughs, and reacts to our emotions, but doesn't imitate gestures or sounds. I can't tell if anything we say is understood.

Seems way behind friends kids and all the milestone lists I see. We have a ped appt in a few weeks, but we had birth complications so I'm just nervous. Talk me off a ledge y'all.