CUA: How does BAPI_USER_CREATE1 creates the data in Central and child system

HI All,

An existing program is using BAPI_USER_CREATE1 in child system. BAPI will create the user in both central and child system. We are just passing password/user/last name.But when am checking in su01 in both central and child system, the first name is also available.

My question is, from where this first name is obtained in both Central and child system? Is it ALREADY available in Central system(If yes how does it exists in Central system without user being created and where to see it in central system before user being created)?

Kindly help.