Hi,
How are you maintaining the condition record for your JMIP Condition i.e. what is the key combination ?
Have you tried testing by creating a PO with the same tax code SL for the above case after 18.02.2014 and whether the rates are populated correctly if you change the PO Creation dates ?
Did you try to use J1IEX capture option ? Just try 1, 2 and 3 step options for posting the excise.
Also in the above SAP note - 1147512 it is mentioned that to use the user exit 'J1I7_USEREXIT_GET_IN_J1IEXGM'. for considering the Goods Receipt posting date for excise rate determination.
Thanks n Regards,