IPC UserExits, Custsomer Account Class, Populate ACCNT_CLS For Vertex

Question

With reference to our landscape: CRM40 w/ IPC40 SP 07 Patch 26.
We are in the process of extending our CRM 40 system for consumer use in Canada. We have been running our US implementation since 2005. In the US we have implemented the java PricingUserExits in order to implement our custom routines.
For Canada however, we have a user exit in R/3 side that contains functionality we need to replicate in our CRM system. This userexit is implemented (based on oss note 302998) in order to populate CH_USER_CHANGED_FIELDS-ACCNT_CLS field. The  userexit name is EXIT_SAPLFYTX_USER_001. Below is the code segment:
  select single gform
         into ch_user_changed_fields-accnt_cls
         from kna1
         where kunnr = ch_user_changed_fields-accnt_no. "Ship-To
On the r/3 system, the ACCNT_CLS value is passed to Vertex which in turn handles the proper tax determination.
I have researched OSS, SDN and Web as well as my own trial and error coding in java user exits ItemTaxUserExit and DocumentTaxUserExit in order to bind ACCNT_CLS attribute along with a hard coded value. However the functionality/result I expect is as if Vertex is not receiving or recognizing the value. I can bind the attribute ACCNT_CLS without error. Here is the simple explanation of my enhancement:
In ItemTaxUserExit.addAttributeBindings  along with some conditional logic, I am invoking the following method calls against object itemUserExitAccess and document
itemUserExitAccess.addHeaderAttributeBinding("ACCNT_CLS","GW");
document.addHeaderAttributeBinding("ACCNT_CLS","GW");
in ItemTaxUserExit.determineRelevantAttributes I have specified the following:
return new String[] { PricingCustomizingConstants.AttributeNames.product_taxability_type, "ACCNT_CLS" };
One thing to note is the ACCNT_CLS is not one of the PricingCustomizingConstants.AttributeNames so I have explicitly used ACCNT_CLS.
I also output the value of this attribute to the log to verify it has been set and contains value. It is successful and has value
Log.getInstance().log(this,Severity.DEBUG,"accntclsBinding was not null " + accntclsBinding.getName() + " = " + accntclsValue.getValue() ,null);
I feel I am heading in the right direction but possibly off the beaten path. I have tried to bind bogus attributes and receive a java null pointer exception so binding ACCNT_CLS successfully is a good thing. But why it is not communicated to Vertex.
I found two oss notes 673222 and 586939. Do you feel these are applicable and an appropriate for resolving my issue?
Any advise and direction you can provide would be greatly appreciated.

Answer 1