"not yet expired" is correct and usable in written English. You can use it when you want to say that something has not ended or is still in effect. For example, "The membership is not yet expired, so I can still go to the gym.".
The third member's term has not yet expired.
It ordered that the five members whose terms had not yet expired be reinstated and that a special election be held to fill the four remaining seats.
His chancellor, Mercurino Gattinara, summoned the Castilian Cortes to Santiago in northwestern Spain (April 1520) to demand more money, even though the former grant had not yet expired.
Though from my personal standpoint I know for a certainty that the meter had not yet expired, please accept my expression of deep regret at this unfortunate incident.
The timing of the filing was a bit of a surprise, because the 30-day grace period on the company's bond-interest payment hadn't yet expired.
Whether your contract term hasn't yet expired, or you just don't feel compelled to upgrade to the latest device, we've got a giveaway bundle that'll make you happy to keep using your iPhone 3G or 3GS! Headphones, docks, skins, portable power, and more: this giveaway is valued at more than $400.
Troubleshoot movie rentals that haven't yet expired.
When I feel like I can't trust my brain 100%, Ludwig really comes in handy. It makes me translate and proofread faster and my output more reliable.
Claudia Letizia
Head Translator and Proofreader @ organictranslations.eu