Validating Distribution Account through Form Personalization

Hi,

I'm trying to use Form Personalization to prevent user entry of invoice distributions with different SEGMENT1 in their Account field.

If it is a brand new invoice and so no distribution records have been saved yet to the database, what condtion may I specify in my Form Personalization function?

I figured I can use WHEN-NEW-RECORD-INSTANCE trigger event. Then for the condition, I basically need to compare the newly entered SEGMENT1 account with the previously entered SEGMENT1. But if the previously entered SEGMENT1 have not yet been saved to the database, how can I retrieve their values through Form Personalization?