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The MS-102 exam is only part of the requirements for the Microsoft 365 Administrator Expert certification. You must also hold one of the prerequisite active associate certifications. https://learn.microsoft.com/en-us/credentials/certifications/m365-administrator-expert/#certification-prerequisites
Exams do not expire so there is no 12-month limit, so you have been misinformed. However, exams can be retired, the certification itself can be retired, and the prerequisite certifications can be changed. In fact, MS-102 replaced MS-100/101 and the prerequisites for the Microsoft 365 Administration certification have changed several times over the past few years. So you need to take one of the prerequisite exams asap.
With the focus to AI and Copilot, Microsoft is retiring many exams and certifications this year (https://techcommunity.microsoft.com/blog/skills-hub-blog/the-ai-job-boom-is-here-are-you-ready-to-showcase-your-skills/4494128) although nothing has yet been announced regarding the Modern Work certifications.