Tax number not populating in IDOC

Hi All,

I am having one sales order no. where in sold-to-party the fields Telex number and Teletex number are empty. And for the idoc generated the field Tax number1(STCD1) is getting populated. For another sales order no. this is vice versa. How to find the condtion why it is not populating for the second condition. Awaiting for your replies.

Thanks,

Harihta