I had $1200 in flight credit from a cancelled flight that was going to expire before I could use it. So I used it to buy a cheap $35 one way ticket and the remaining value was issued as trip credit that will expire one year from the date I purchased the cheap ticket. Now that expiration date for the trip credit is approaching. If I use the trip credit to buy another cheap ticket will the remaining value be issued as trip credit with a new expiration date another year out, or will the expiration date of the first trip credit remain in affect?