Are you perhaps..
A social security number (SSN)/the social security system in the United States?
I arise well after 3
According to Wikipedia, over 25 million numbers were issued in the first three months, which is still a fraction of the entire population. Hence it would take well over 3 (months) for the system as it is today to arise.
and there are 9 that make me.
A social security number has 9 digits.
My world has random form. For me, too, that's the norm.
Any one SSN looks like a random string of numbers.
I feel incomplete and I know that I am.
Not everyone in the United States has one due to religious objections, etc.
Please look me up sometime. This isn't a scam.
It is important to know your SSN. Also, as with pretty much any country-wide identification system, it has been used for and in scams.
I'll provide some ID with high hopes you'll agree. 246-89-0641
Google tells me that this is an example of an SSN.