I am having to cancel a nonrefundable main cabin ticket. According to all I have read, I will receive a trip credit dated from the original date of issuance of the ticket.

I will likely be using the trip credit to book another ticket in the next few weeks, but it will be a less expensive ticket.

Am I correct in assuming that I will receive another trip credit for the residual amount, with the original date of issuance?

Thanks.