Job Manager: Customer No. field on Item table?

Hello,
i searched this on the forum but found zilch. i also looked through whatever documentation is left from the times before i worked for my current employer and found nothing.

question:
We purchased Job Manager from Cost Control. on the Item table, i see a field "Customer No." listed with a field No. in sequence with other Job Manager fields. I assume that means they added this field. Further, I see the field in a screen shot of the Item Card in one of their tutorial videos (but they do not talk about it). Thus, i'm failry sure it is their field.

now, this field is not exposed to our end users so nobody knows about it or what it is supposed to do. in my test system, i added the field to the item card and defined a customer for a custom part we sell for a single client. I then created a Job to build this part but the bill-to/sell-to customer on the Job record is still undefined.

does anyone know, off hand, what this field is supposed to be used for if it doesn't automatically flow down to the Job?