Do DLC & Expansion codes that have no indicated expiration dates never expire?

Normally if there's no date then it shouldn't expire, but i wouldnt risk it. If you're giving away the code, then i'd suggest not holding onto it for too long.

The game codes do not expire but keep in mind that you can leave the store and in that case if you could lose it.

Generally trial codes will have an expiration date on them, but all the other codes that I have received haven't had one on them and they still have worked even like two years of me receiving them. I actually had a trial code which had an expiration date
on it, but when I used it a year and a half after it had expired, it still worked. Thank goodness, because it was for three months of Game Pass. Apparently I need to redeem codes a little quicker, LOL.

If the codes don't have an expiration date, then they typically don't expire. However, if the content has been delisted from the marketplace, the code may no longer work so you may need to check that although for a game like that they're probably still
available.

Physical cards will have an expiration date on the back. Digital codes meanwhile do not have an expiration date, but there are exceptions to that rule. Promotional codes will expire.... sometimes. Reason i say “sometimes” is it depends.... case in point
I bought some used games from a pawn shop & i was wondering if the DLC codes were used & there was a 2 week Xbox Live code in there as well. I entered them both & they were never redeemed, but they had expiration dates on them that had already passed.

If you’re buying online then the digital codes shouldn’t have an expiration date.... but I wouldn’t just sit on it either.