Note: I write comments and  explanations in brackets.

First of all I have to say I would draw "Data Model for a Part" another way (comparing to drawn on ProductEngineering/plm_parts.htm).
I'd draw an arrow from Vendor to Manufactured Part instead of arrow from Manufactured Part to Vendor. The same thing with a model on ProductEngineering/Sourcing.htm page. An arrow should go from Vendor to Manufactured Part and not from Manufactured Part to Vendor.
Because this corresponds to Data Model I see in Innovator. (Check Vendor and Manufactured Part to see the dependencies.)

You see Part AML relationship and related Manufactured Part on the AML tab. Manufacturer is a property of a Manufactured Part. Thus you see it on the tab.

 However according to the actual Innovator Data Model the Manufactured Part is a related item in Vendor -> Manufactured Part dependency. The tab (this is a "relationships grid" UI component) does not provide an ability to display "where used" for a related item (related item is an item referenced bya  relationship via related_id property).

If you need this you may do the following:
1) add a new federated property my_vendors to Manufactured Part ItemType (set data_type=federated);
2) implement onAfterGet server event handler for Manufactured Part ItemType.
    in that event handler for each Manufactured Part find where that used (who are vendors) and populate the my_vendors property joining vendors' names with ";" or new line;
3) ensure Hidden2 is false for property my_vendors in Manufactured Part ItemType definition;

When done you'll see a new column my_vendors in AML tab populated with data you set in onAfterGet handler.
The column will be read-only because of the data type (federated).