Billing date change in vf04 but not in vf01

Dear sd legends plz let me know

i know how date will come to billing in VF01

From in vl01n -- goods issue date

otherwise if we keep billing date in header level -- processing data tab -- Billing date is there if we keep particulate date same date will come to VF01

We cant change billing date in VF01 ( But if keep 11 in copy control at vtfl -- vbrk/vbrp then user can change billing date in vf01) i know this ...

   In my Clint system i have seen in vf04 , we can do modify billing date but no 11 In copy control vtfl

so my doubt is in vf01 not possible generally to change the date in case if you dont maintain 11 but how it possible in VF04

i Am thinking any new enhancement they have done to change the billing date in vf04 like goods issue date is 10th but we can change to 12th or 13th

and no service rendered date maintained   

So finally my doubt is in case if they maintained some enhancement to particulate scenario how to find    ? 

Thanks a lot