Roberto -
Standard Data Directives run as the very last event before the AppServer completes and it runs once regardless of how many records were updated. With the way your code is written, it appears to me that you will be working with the First record updated but the BPMData value will be for the Last record updated.
As noted - BPMData is valid for the complete execution chain on the AppServer but it is a single record so you cannot use it in the way you are attempting.