I was thinking maybe after roxas was introduced in viertual twilight town, Namine started to take away roxas memories and returning them to sora
Since this process will take some time, maybe Namine implanted some memories into Roxas, and blocked his memories from the days in the organization.
Soo when Roxas wakes up in day 259/ The first day Its just another day on his "normal life" where he has friends and goes to school and etc. Even when none of that happened.