A customer heading above a list of orders does not prove that the list belongs to that customer. If the embedded list shows unrelated records, inspect how the two forms are linked before changing the order data.

Use a copied desktop Access database with fictional customers A and B. Give A orders A17 and A18, and B order B42. Keep CustomerID and order identifiers visible during the check. The different set sizes make navigation errors easier to detect than two customers with similar-looking orders.

Select the embedding control

Microsoft distinguishes the subform control from the form object it displays. Source Object chooses the embedded object. Link Master Fields identifies the main-form field, while Link Child Fields identifies the matching child field. These links restrict the displayed child records to the current parent; an unlinked subform can display all orders.

Open the main form in Design View and click the subform control once. Press F4, choose the Property Sheet's Data tab, then use the build button beside Link Child Fields. In Subform Field Linker, select the actual master and child fields. For example, CustomerID on the parent might match CustomerRef in the order source; the names need not be identical.

If the intended field is unavailable, Microsoft advises checking the main or child form's Record Source. A query used by that form must include the linking field in its results. Do not substitute a friendly customer name merely because the real key was omitted from the source query.

Verify the child sets in both directions

Save the main form and switch to Form View. Navigate to A, then B, then A again. Expect A17/A18, then B42, then A17/A18. Check the order identifiers themselves as well as the row count and displayed customer heading.

Also inspect a fictional customer with no orders. An empty child set is the correct result for that customer; it should not retain the previous customer's orders to fill the space. Keep the test focused on viewing existing records until the linking design is understood.

For the actual database, confirm that the selected key fields express the intended relationship and that both record sources contain the required data. The useful outcome is a repeatable parent-to-child navigation check. Renaming the embedded form or editing customer labels would not by itself establish the missing link.

Sources: Microsoft: linked subforms.