VG01 Group number for delivery

Dear Expert,

I'm not understand how the Group number for delivery be allocated and generated.

As checked in VG03, the group numbers are in requence but the date and time generated were not be in accending.

E.g. group number 707172 created on 24.07.2013 14:59:29 --> this no 707172 is smaller but created later than 707178 which is bigger

but group number 707178 created on 24.07.2013 14:25:55

User understanding is the number should in accending order according as per date and time (first come first serve).

Please advice any doc that I can refer and show user about the logic. Thanks.

Thanks.

Aw