A vehicle returns to the workshop. Its mileage has changed, so the current vehicle record changes too. That is ordinary maintenance of useful information. It becomes a problem when an invoice from an earlier visit starts showing the new mileage.
That problem appeared in JNC Suite: an earlier invoice view read current vehicle information. The relationship in the database was valid, but the document no longer described the visit it was supposed to record.
Decide what the document represents
The correction was to preserve customer and vehicle details when the invoice was created. The customer and vehicle records could continue to evolve. The issued document kept the details that belonged to its own moment.
This is a product decision expressed through the data model. A customer page answers a question about the current relationship. An old invoice answers a question about work that already happened. Both can refer to the same vehicle without using the same changing values for every field.
Follow the meaning through the workflow
JNC Suite connects estimates, assignments, parts, labor, and invoices. Estimates retain their line items, discounts, and tax as they become invoices. Preserving those details makes the document part of the job's history, rather than a view assembled from whatever the latest records happen to contain.
The useful question is simple: should this screen show what is true now, or what was recorded then? An interface can look the same either way. Its answer should be deliberate.