Difference between GR & Subsequent Adjustment

Hi,

We have done GR (100) against IBDN (qty 100).

Return to vendor 80 - (122 Mvt) and 20 - 321 (Mvt) was done by mistake (at the time of giving QM UD)

20 qty has already been consumed and now the user wants to have only40 Ret to vendor and 40 additional qty unrestricted.

Since 20 unrestricted stock has already been consumed and their is no stock in unrestricted it is not getting possible to reverse the initial 122 and 321 Mvt.

One way solve this is to do is do good receipt again or perform subsequent adjustment.

Consultants are suggesting us to go with subsequent adjust.

Please suggest what is the difference between Subsequent Adjustment and MIGO GR

Regards

Amlan C