I had mixed results in doing this recently. I had read about this trick on this forum, and as I had 2 credits expiring on the 19th of this month. I booked two separate tickets with the two separate eCredits, with a price slightly higher than each one. One of the new tickets then had an expiration date of 60 days from date of purchase and one had an expiration date of 1 year after purchase (15May2024 and 15Mar2025). Not sure why there was a difference in the results, when I did the same thing on both.