@bigpaul Fun Fact: these dates are averages and the milestones aren't binary.
Its not like your kid is suddenly going to say "mama" at 00:01 on the day leading into the correct month. Its a slow process and all milestones are incremental.
E.G - your kid isn't sitting up at 9 months. but can they crawl across the room? on their bellies or hands and knees?
Every kid is different and will hit milestones at different times. but short of any major disability, they'll get there eventually.
Don't stress. Be patient.
Signed, A dad whose kid only started "crawling" at 9 months