This month mark's officially X-23's Ten Year Anniversary in being published. Her first appearance back in NYX v1 issue 3 was released on December 10th, 2003 but the published date for that issue itself is February 2004. So Marvel has her officially marked as established in 2004.
This isn't uncommon for comics. Comics are always released prior to what's considered their published date. Usually it's the month prior, but in many instances it can be upwards of 2-3 months prior.
X-23 herself because of all these different factors has several birthdays really.
We have the date her idea was conceived that's been lost to time except for maybe internet database archival sites. (The site the original interview was on that she blossomed from has long since been taken off the internet.)
The date her first animated appearance episode was given the okay to be scripted and designed. Probably also lost over time.
The date her episode of X-Men Evolution first aired. August 2nd, 2003.
The date she was given the green light to be added to 616 Marvel.
The date her 616 Marvel design was finalized as it was altered from her X-Men Evolution appearance.
The date her first comic appearance in 616 Marvel was released to stores. December 10th, 2003.
The date her first comic appearance in 616 Marvel was considered published. February 2004.
She's the girl with 7 birthdays. A tongue in cheek reference to her complicated history made in her own second origin miniseries that also makes reference to her Facility spec-ops paper trails for various missions. You could say that Laura Kinney literally has a full birthday week. (Cause you know, there's 7 days in a week... Okay, okay, I know. Bad pun.)