you can increase the accuracy of the CO data by using 
Validation and substitution.in validation and substitution 
the R/3 system checks for the data entered meets one or 
more conditions that you defined.these checks take place 
during the data entry., thereby ensuring that only valid 
data is entered.

if condiions specified are not met for executing business 
transaction,R/3 systems displays a user defined message.

you can carry validation checks when making 
substitution.however if conditions are met for 
substitution,R/3 system substitutes the value with others 
defined by you without informing you of this change.

Validation has priority over substitutions.

Hi,
In the SAP system, nearly all input values are validated by
a program or against tables or master files. Since some
types of validations cannot be standardized, you can use the
validations program to create validations for your specific
requirements.
The validation function enables you to check values and
ranges of values as they are being entered in the SAP
system. Validation rules are stored in the Rule Manager. As
data is entered into the system, the Integration Manager
validates the data against the validation rules. Because
data is validated before it is actually posted, only valid
information is posted to the FI-SL application component.
Many values that you enter into the SAP system are
automatically checked against standard validation rules.
The system validates account numbers against a master file
or checks that a ledger is assigned to a local company code.
You use validations when you want to create a user-defined
Boolean statement to validate an entry in a way that is not
defined for the standard system. FI-SL validations allow you
to create your own Boolean statements without making any
changes to the standard system.

Substitution rules are stored in the Rule Manager. When data
is entered in the system, it is substituted by the
Integration Manager. Substitution occurs before the data is
added to the FI-SL summary tables.
In FI-SL substitution, the values entered into the SAP
system are validated against a prerequisite defined by the
user. When the prerequisite is met, the system replaces the
values entered with substitute values, and the substitute
values are transferred into the FI-SL application component.
The system first performs validation and then substitution.
This gives you the opportunity of having the system validate
values that are to be substituted.

Hopefully this would be helpful for you all.
Regards.