The PassPlus contract is effective for 13 months. You are afforded GS status during those 13 months. If you start your contract in March 2023, then the contract ends in March 2024. Also, remember that premier status is based on a Feb 1 to Jan 31 year. Therefore, on March 2023, you are eligible for GS, and the nomination is good from March 2023 to Jan 2024. But since your PassPlus contract is still valid from Feb 2024 to March 2024, the terms of the PassPlus agreement still afford you GS status during that period, so they will give you another nomination come Feb 2024, which is valid until Feb 2025. They count on you becoming a repeat customer, and they need to establish the process to remove your GS status and downgrade you to 1K once your contract is up. Taking away status or your MP account doesn't happen unless you did something egregious like selling your PlusPoints like these idiots on eBay.

You can cancel any ticket (presumably purchased using your PassPlus) and receive future flight credits for it. It's usually a year from the cancellation date, but the pandemic has kicked the expiration goal post to the end of next year. Lather, rinse, repeat.