I tested the form and found a few "inconsistencies" and the Postal Code field was not the only one.

Otherwise, more than a year ago I had read elsewhere that AC's refund services is outsourced to a huge American conglomerate. I certainly felt that was the case when I had to communicate with a CSR.

The URL of the form linked by OP (highlight mine)

https://refundservices.business.conduent.com/AirCanada/Refunds/Create

just saying.....and it may, or may not matter