This is weird, been using Bartender for years but never realized that the named fields in a text file are only named at design time; at run time it uses field positioning.

MATERIAL|SIZE|LOCATION
Rock|Big|USA

With bartender you add this file as a "database", you can then drag around fields like size, location. However, at run-time the field names do not matter. This source file will print exactly as well:

CHEVY|BANANA|RED
Rock|Big|New York

Moreover, if you have a template that references only the SIZE field (second field) and then at production feed it a flat file with MATERIAL missing, and only two fields, it will end up printing LOCATION.