Should I be calm?

I was talking to an entirely random stranger and it led me to question if I should be worrying/panicking/alarming more about Chiron.  Somehow we started talking about kids (grand kids in her case) and what they did and I mentioned that while Chiron loves holding fingers or a chair and standing, he doesn't sit.  He will sit in a bumbo, but try and persuade him to adopt a tripod position sitting on his own and you will have a locked-hip baby on your hands.

I've always kind of just thought that he doesn't like sitting.  And he can do things in his own order and it's all fine.  He's an alert, happy, smart, talkative little boy. 

But can I have this attitude given his prematurity?  Am I taking a luxury that we don't have?

Writing this has made me go do a quick google of developmental milestones and I think he's doing ok.  He definitely is inconsistent in his skills, but sitting is the only one that is behind his adjusted age and he even is hitting some at his chronological age.

Things he can do:
Roll in both directions
Stand holding things
Support his whole weight on his legs
Transfer objects between hands and mouth
Pull things toward him
Use a pincer grasp
Laugh/giggle/coo with both consonants and vowels

Things he doesn't do:
Sit on his own (either with or without support of his hands)
Scoot when laying on his belly
Doesn't chain sounds or combine syllables
Pull self up to standing position
Clearly recognize his name

He has an appointment with the pediatrician next Friday, so I will go ahead and get her feedback on this, but I think I probably am ok continuing with my being calm.