Hi Andrew,
Kindly find the screeshots below
This mandatory account assignments setting to give instructions that when ever you are using this G/L the system prompts you to give a costcenter
Below setting can be done for automatic determination of the Cost Center
For you reference in the below manual entry, i have only entered the G/L account and the cost center is defaulting automatically
Addtional Control
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May be if the users have posted to wrong cost center for this G/L then you may try creating addtional Account Deterination Group as mentioned below and once the distribution rule is created you can run the distribution so that if a different cost center is used for this G/L in Question then with the help of this Distribution run you can move the costs to the correct cost centers.
Thanks
Lokesh Sharma