same external ID for multiple partners

Shall we use the same external ID value for multiple partners say as GOAL SAP CODE and user defined 1 ?

This question seems like it refers to B2B or Trading Networks. Recommend you re-post in the B2B forum:
http://tech.forums.softwareag.com/techjforum/forums/show/184.page

If this is about TN ID: The idea is o distinguish partners by this ID, so having it a fixed value contradicts this idea.